This CSS module defines a two-dimensional grid-based layout system, optimized for user interface design. In the grid layout model, the children of a grid container can be positioned into arbitrary slots in a flexible or fixed predefined layout grid.

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The following features are at-risk, and may be dropped during the CR period:

1. Introduction and Overview

Grid layout contains features targeted at web application authors. The grid can be used to achieve many different layouts. It excels at dividing up space for major regions of an application, or defining the relationship in terms of size, position, and layer between parts of a control built from HTML primitives.

Like tables, grid layout enables an author to align elements into columns and rows, but unlike tables, grid layout doesn’t have content structure, and thus enables a wide variety of layouts not possible with tables. For example, the children of a grid container can position themselves such that they overlap and layer similar to positioned elements.

In addition, the absence of content structure in grid layout helps to manage changes to layout by using fluid and source order independent layout techniques. By combining media queries with the CSS properties that control layout of the grid container and its children, authors can adapt their layout to changes in device form factors, orientation, and available space, without needing to alter the semantic nature of their content.

1.1. Background and Motivation

Application layout example requiring horizontal and vertical alignment.

As websites evolved from simple documents into complex, interactive applications, tools for document layout, e.g. floats, were not necessarily well suited for application layout. By using a combination of tables, JavaScript, or careful measurements on floated elements, authors discovered workarounds to achieve desired layouts. Layouts that adapted to the available space were often brittle and resulted in counter-intuitive behavior as space became constrained. As an alternative, authors of many web applications opted for a fixed layout that cannot take advantage of changes in the available rendering space on a screen.

The capabilities of grid layout address these problems. It provides a mechanism for authors to divide available space for layout into columns and rows using a set of predictable sizing behaviors. Authors can then precisely position and size the building block elements of their application by into grid areas defined by these columns and rows. Figure 1 illustrates a basic layout which can be achieved with grid layout.

1.2. Adapting Layouts to Available Space

Five grid items arranged according to content size and available space.

Growth in the grid due to an increase in available space.

Grid layout can be used to intelligently reflow elements within a webpage. Figure 2 represents a game with five major areas in the layout: the game title, stats area, game board, score area, and control area. The author’s intent is to divide the space for the game such that:

The stats area always appears immediately under the game title.

The game board appears to the right of the stats and title.

The top of the game title and the game board should always align.

The bottom of the game board and the stats area align when the game has reached its minimum height, but otherwise the game board will stretch to take advantage of all the screen real-estate available to it.

The score area should align into the column created by the game and stats area, while the controls are centered under the board.

As an alternative to using script to control the absolute position, width, and height of all elements, the author can use grid layout, as shown in Figure 3. The following example shows how an author might achieve all the sizing, placement, and alignment rules declaratively.

Note that there are multiple ways to specify the structure of the grid and to position and size grid items, each optimized for different scenarios. This example illustrates one that an author may use to define the position and space for each grid item using the grid-template-rows and grid-template-columns properties on the grid container, and the grid-row and grid-column properties on each grid item.

#grid { display : grid ; /* Two columns: the first sized to content, the second receives * the remaining space, but is never smaller than the minimum * size of the board or the game controls, which occupy this * column. */ grid - template - columns : auto minmax ( min - content , 1 fr ); /* Three rows: the first and last sized to content, the middle * row receives the remaining space, but is never smaller than * the minimum height of the board or stats areas. */ grid - template - rows : auto minmax ( min - content , 1 fr ) auto } /* Each part of the game is positioned between grid lines by * referencing the starting grid line and then specifying, if more * than one, the number of rows or columns spanned to determine * the ending grid line, which establishes bounds for the part. */ #title { grid - column : 1 ; grid - row : 1 } #score { grid - column : 1 ; grid - row : 3 } #stats { grid - column : 1 ; grid - row : 2 ; align - self : start } #board { grid - column : 2 ; grid - row : 1 / span 2 ; } #controls { grid - column : 2 ; grid - row : 3 ; justify - self : center } <div id= "grid" > <div id= "title" > Game Title </div> <div id= "score" > Score </div> <div id= "stats" > Stats </div> <div id= "board" > Board </div> <div id= "controls" > Controls </div> </div>

1.3. Source-Order Independence

An arrangement suitable for “portrait” orientation.

An arrangement suitable for “landscape“ orientation.

Continuing the prior example, the author also wants the game to adapt to the space available on traditional computer monitors, handheld devices, or tablet computers. Also, the game should optimize the placement of the components when viewed either in portrait or landscape orientation (Figures 4 and 5). By combining grid layout with media queries, the author is able to use the same semantic markup, but rearrange the layout of elements independent of their source order, to achieve the desired layout in both orientations.

The following example leverages grid layout’s ability to name the space which will be occupied by a grid item. This allows the author to avoid rewriting rules for grid items as the grid’s definition changes.

@media ( orientation : portrait ) { #grid { display : grid ; /* The rows, columns and areas of the grid are defined visually * using the grid-template-areas property. Each string is a row, * and each word an area. The number of words in a string * determines the number of columns. Note the number of words * in each string must be identical. */ grid - template - areas : "title stats" "score stats" "board board" "ctrls ctrls" ; /* Columns and rows created with the template property can be * assigned a sizing function with the grid-template-columns * and grid-template-rows properties. */ grid - template - columns : auto minmax ( min - content , 1 fr ); grid - template - rows : auto auto minmax ( min - content , 1 fr ) auto } } @media ( orientation : landscape ) { #grid { display : grid ; /* Again the template property defines areas of the same name, * but this time positioned differently to better suit a * landscape orientation. */ grid - template - areas : "title board" "stats board" "score ctrls" ; grid - template - columns : auto minmax ( min - content , 1 fr ); grid - template - rows : auto minmax ( min - content , 1 fr ) auto } } /* The grid-area property places a grid item into a named * region (area) of the grid. */ #title { grid - area : title } #score { grid - area : score } #stats { grid - area : stats } #board { grid - area : board } #controls { grid - area : ctrls } <div id= "grid" > <div id= "title" > Game Title </div> <div id= "score" > Score </div> <div id= "stats" > Stats </div> <div id= "board" > Board </div> <div id= "controls" > Controls </div> </div>

1.4. Grid Layering of Elements

A control composed of layered HTML elements.

In the example shown in Figure 6, the author is creating a custom slider control. The control has six parts. The lower and upper labels align to the left and right edges of the control. The track of the slider spans the area between the labels. The lower and upper fill parts touch beneath the thumb, and the thumb is a fixed width and height that can be moved along the track by updating the two flex-sized columns.

Prior to the introduction of grid layout, the author would have likely used absolute positioning to control the top and left coordinates, along with the width and height of each HTML element that comprises the control. By leveraging grid layout, the author can instead limit script usage to handling mouse events on the thumb, which snaps to various positions along the track as the grid-template-columns property of the grid container is updated.

#grid { display : grid ; /* The grid-template-columns and rows properties also support * naming grid lines which can then be used to position grid * items. The line names are assigned on either side of a column * or row sizing function where the line would logically exist. */ grid - template - columns : [ start ] auto [ track - start ] 0 . 5 fr [ thumb - start ] auto [ fill - split ] auto [ thumb - end ] 0 . 5 fr [ track - end ] auto [ end ]; } /* The grid-placement properties accept named lines. Below the * lines are referred to by name. Beyond any * semantic advantage, the names also allow the author to avoid * renumbering the grid-column-start and grid-row-start properties of the * grid items. This is similar to the concept demonstrated in the * prior example with the grid-template-areas property during orientation * changes, but grid lines can also work with layered grid items * that have overlapping areas of different shapes like the thumb * and track parts in this example. */ #lower-label { grid - column - start : start } #track { grid - column : track - start / track - end ; justify - self : center } #upper-label { grid - column - end : end ; } /* Fill parts are drawn above the track so set z-index to 5. */ #lower-fill { grid - column : track - start / fill - split ; justify - self : end ; z-index : 5 } #upper-fill { grid - column : fill - split / track - end ; justify - self : start ; z-index : 5 } /* Thumb is the topmost part; assign it the highest z-index value. */ #thumb { grid - column : thumb - start / thumb - end ; z-index : 10 } <div id= "grid" > <div id= "lower-label" > Lower Label </div> <div id= "upper-label" > Upper Label </div> <div id= "track" > Track </div> <div id= "lower-fill" > Lower Fill </div> <div id= "upper-fill" > Upper Fill </div> <div id= "thumb" > Thumb </div> </div>

2. Grid Layout Concepts and Terminology

In grid layout , the content of a grid container is laid out by positioning and aligning it into a grid. The grid is an intersecting set of horizontal and vertical grid lines that divides the grid container’s space into grid areas, into which grid items (representing the grid container’s content) can be placed. There are two sets of grid lines: one set defining columns that run along the block axis (the column axis ), and an orthogonal set defining rows along the inline axis (the row axis ). [CSS3-WRITING-MODES]

Grid lines: Three in the block axis and four in the inline axis.

2.1. Grid Tracks and Cells

Grid track is a generic term for a grid column or grid row—in other words, it is the space between two adjacent grid lines. Each grid track is assigned a sizing function, which controls how wide or tall the column or row may grow, and thus how far apart its bounding grid lines are.

A grid cell is the similar term for the full grid—it is the space between two adjacent row and two adjacent column grid lines. It is the smallest unit of the grid that can be referenced when positioning grid items.

<style type="text/css"> #grid { display: grid; grid-template-columns: 150px 1fr; /* two columns */ grid-template-rows: 50px 1fr 50px /* three rows */ } </style> In the following example there are two columns and three rows. The first column is fixed at 150px. The second column uses flexible sizing, which is a function of the unassigned space in the Grid, and thus will vary as the width of the grid container changes. If the used width of the grid container is 200px, then the second column 50px wide. If the used width of the grid container is 100px, then the second column is 0px and any content positioned in the column will overflow the grid container

2.2. Grid Lines

Grid lines are the horizontal and vertical dividing lines of the grid. A grid line exists on either side of a column or row. They can be referred to by numerical index, or by an author-specified name. A grid item references the grid lines to determine its position within the grid using the grid-placement properties.

2.3. Grid Areas

A grid area is the logical space used to lay out one or more grid items. It is bound by four grid lines, one on each side of the grid area, and participates in the sizing of the grid tracks it intersects. A grid area can be named explicitly using the grid-template-areas property of the grid container, or referenced implicitly by its bounding grid lines. A grid item is assigned to a grid area using the grid-placement properties.

<style type="text/css"> /* using the template syntax */ #grid { display: grid; grid-template-areas: ". a" "b a" ". a"; grid-template-columns: 150px 1fr; grid-template-rows: 50px 1fr 50px } #item1 { grid-area: a } #item2 { grid-area: b } #item3 { grid-area: b } /* Align items 2 and 3 at different points in the Grid Area "b". */ /* By default, Grid Items are stretched to fit their Grid Area */ /* and these items would layer one over the other. */ #item2 { align-self: start } #item3 { justify-self: end; align-self: end } </style>

A grid item’s grid area forms the containing block into which it is laid out. Percentage lengths specified on a grid item resolve against this containing block. Percentages specified for margin-top, padding-top, margin-bottom, and padding-bottom on a grid item resolve against the height of its containing block, rather than the width (as for blocks).

This margin/padding behavior is disputed. (see discussion)

Grid items placed into the same grid area do not directly affect each other’s layout. Indirectly, a grid item can affect the position of a grid line in a column or row that uses a content-based relative size, which in turn can affect the position or size of another grid item.

3. Grid Containers

Name: display New values: grid | inline-grid

grid This value causes an element to generate a block-level grid container box. inline-grid This value causes an element to generate an inline-level grid container box.

A grid container establishes a new grid formatting context for its contents. This is the same as establishing a block formatting context, except that grid layout is used instead of block layout: floats do not intrude into the grid container, and the grid container’s margins do not collapse with the margins of its contents. The contents of a grid container are laid out into a grid, with grid lines forming the boundaries of each grid items’ containing block. The overflow property applies to grid containers.

Grid containers are not block containers, and so some properties that were designed with the assumption of block layout don’t apply in the context of grid layout. In particular:

the column-* properties in the Multi-column Layout module [CSS3COL] have no effect on a grid container.

float and clear have no effect on a grid item. (However, the float property still affects the computed value of display on children of a grid container, as this occurs before grid items are determined.)

vertical-align has no effect on a grid item.

the ::first-line and ::first-letter pseudo-elements do not apply to grid containers, and grid containers do not contribute a first formatted line or first letter to their ancestors.

If an element’s specified display is inline-grid and the element is floated or absolutely positioned, the computed value of display is grid. The table in CSS 2.1 Chapter 9.7 is thus amended to contain an additional row, with inline-grid in the "Specified Value" column and grid in the "Computed Value" column.

3.2. Sizing Grid Containers

A grid container is sized using the rules of the formatting context in which it participates. As a block-level box in a block formatting context, it is sized like any other block-level box that establishes a formatting context, with an auto inline size calculated as for in-flow block boxes. As an inline-level box in an inline formatting context, it is sized as an atomic inline-level box (such as an inline-block). In both inline and block formatting contexts, the grid container’s auto block size is its max-content size. The block layout spec should define this?

The max-content size of a grid container is the sum of the grid container’s track sizes in the appropriate axis, when the grid is sized under a max-content constraint.

The min-content size of a grid container is the sum of the grid container’s track sizes in the appropriate axis, when the grid is sized under a min-content constraint.

See [CSS3-SIZING] for a definition of the terms in this section.

4. Grid Items

The contents of a grid container consists of zero or more grid items : each child of a grid container becomes a grid item, and each contiguous run of text that is directly contained inside a grid container is wrapped in an anonymous grid item. However, an anonymous grid item that contains only white space is not rendered, as if it were display:none.

<div style="display:grid"> <!-- grid item: block child --> <div id="item1">block</div> <!-- grid item: floated element; floating is ignored --> <div id="item2" style="float: left;">float</div> <!-- grid item: anonymous block box around inline content --> anonymous item 3 <!-- grid item: inline child --> <span> item 4 <!-- grid items do not split around blocks --> <div id=not-an-item>item 4</div> item 4 </span> </div> Examples of grid items:

The display value of a grid item is blockified: if the specified display of an in-flow child of an element generating a grid container is an inline-level value, it computes to its block-level equivalent. (See CSS2.1§9.7 [CSS21] and CSS Display [CSS3-DISPLAY] for details on this type of display value conversion.)

Some values of display trigger the generation of anonymous boxes. For example, a misparented table-cell child is fixed up by generating anonymous table and table-row elements around it. [CSS21] This fixup must occur before a grid container’s children are promoted to grid items. For example, given two contiguous child elements with display:table-cell, an anonymous table wrapper box around them becomes the grid item.

Future display types may generate anonymous containers (e.g. ruby) or otherwise mangle the box tree (e.g. run-ins). It is intended that grid item determination run after these operations.

A grid item establishes a new formatting context for its contents. The type of this formatting context is determined by its display value, as usual. The computed display of a grid item is determined by applying the table in CSS 2.1 Chapter 9.7. However, grid items are grid-level boxes, not block-level boxes: they participate in their container’s grid formatting context, not in a block formatting context.

A grid item is sized within the containing block defined by its grid area similarly to an equivalent block-level box in an equivalently-sized containing block, except that auto margins and the box alignment properties have special effects. (See §11 Alignment and Spacing.)

The auto value of min-width and min-height behaves on grid items in the relevant axis analogously to its behavior on flex items in the main axis. See §4.4 Implied Minimum Size of Grid Items.

Review implications of intrinsic ratio and Grid’s 2D nature.

4.1. Collapsed Grid Items: the visibility property

We want the ability to collapse grid tracks (similar to collapsing flex items or table rows/columns), but we’re not sure exactly how to do it. Ideas welcome, please post them to www-style@w3.org.

4.2. Reordered Grid Items: the order property

The order property also applies to grid items. It affects their auto-placement and painting order.

Grid items can overlap when they are positioned into intersecting grid areas, or even when positioned in non-intersecting areas because of negative margins or positioning. The painting order of grid items is exactly the same as inline blocks [CSS21], except that order-modified document order is used in place of raw document order, and z-index values other than auto create a stacking context even if position is static. Thus the z-index property can easily be used to control the z-axis order of grid items.

Note: Descendants that are positioned outside a grid item still participate in any stacking context established by the grid item.

Drawing order controlled by z-index and source order. <style type="text/css"> #grid { display: grid; grid-template-columns: 1fr 1fr; grid-template-rows: 1fr 1fr } #A { grid-column: 1 / span 2; grid-row: 2; align-self: end; } #B { grid-column: 1; grid-row: 1; z-index: 10; } #C { grid-column: 2; grid-row: 1; align-self: start; margin-left: -20px; } #D { grid-column: 2; grid-row: 2; justify-self: end; align-self: start; } #E { grid-column: 1 / span 2; grid-row: 1 / span 2; z-index: 5; justify-self: center; align-self: center; } </style> <div id="grid"> <div id="A">A</div> <div id="B">B</div> <div id="C">C</div> <div id="D">D</div> <div id="E">E</div> </div> The following diagram shows several overlapping grid items, with a combination of implicit source order and explicit z-index used to control their stacking order.

4.4. Implied Minimum Size of Grid Items

To provide a more reasonable default minimum size for grid items, this specification defines the effects of the min-width/min-height auto value for grid items.

On a grid item whose overflow is visible, when auto is specified on the grid item, the following table gives the minimum size in that dimension:

Specified Size Transferred Size Minimum Size content size ✓ min( specified size , content size ) ✓ min( transferred size , content size ) ✓ ✓ min( specified size , content size )

Where:

Note that while a content-based minimum size is often appropriate, and helps prevent content from overlapping or spilling outside its container, in some cases it is not: In particular, if flex sizing is being used for a major content area of a document, it is better to set an explicit font-relative minimum width such as min-width: 12em. A content-based minimum width could result in a large table or large image stretching the size of the entire content area into an overflow zone, and thereby making lines of text gratuitously long and hard to read. Note also, when content-based sizing is used on an item with large amounts of content, the layout engine must traverse all of this content before finding its minimum size, whereas if the author sets an explicit minimum, this is not necessary. (For items with small amounts of content, however, this traversal is trivial and therefore not a performance concern.)

5. The Explicit Grid

The three properties grid-template-rows, grid-template-columns, and grid-template-areas together define the explicit grid of a grid container. The grid-template property is a shorthand that sets all three at the same time. The final grid may end up larger due to grid items placed outside the explicit grid; in this case, any implicit tracks are sized by the grid-auto-rows and grid-auto-columns properties.

The size of the explicit grid is determined by the larger of the number of rows/columns defined by grid-template-areas and the number of rows/columns sized by grid-template-rows/grid-template-columns. Any rows/columns defined by grid-template-areas but not sized by grid-template-rows/grid-template-columns take their size from the grid-auto-rows/grid-auto-columns properties. If these properties don’t define any explicit tracks, the explicit grid still contains one grid line in each axis.

Numeric indexes in the grid-placement properties count from the edges of the explicit grid. Positive indexes count from the start side (starting from 1 for the start-most explicit line), while negative indexes count from the end side (starting from -1 for the end-most explicit line).

Name: grid-template-columns , grid-template-rows Value: none | <track-list> | subgrid <line-name-list>? Initial: none Applies to: grid containers Inherited: no Percentages: refer to corresponding dimension of the content area Media: visual Computed value: As specified, with lengths made absolute Animatable: no

These properties specify, as a space-separated track list , the line names and track sizing functions of the grid. Each track sizing function can be specified as a length, a percentage of the grid container’s size, a measurement of the contents occupying the column or row, or a fraction of the free space in the grid. It can also be specified as a range using the minmax() notation, which can combine any of the previously mentioned mechanisms to specify separate min and max track sizing functions for the column or row.

The grid-template-columns property specifies the track list for the grid’s columns, while grid-template-rows specifies the track list for the grid’s rows.

The none value indicates that there is no explicit grid; any rows/columns will be implicitly generated, and their size will be determined by the grid-auto-rows and grid-auto-columns properties.

The subgrid value indicates that the grid will align to its parent grid in that axis. Rather than specifying the sizes of rows/columns explicitly, they’ll be taken from the parent grid’s definition.

The syntax of a track list is:

Where:

/* examples of valid track definitions */ grid-template-rows: 1fr minmax(min-content, 1fr); grid-template-rows: 10px repeat(2, 1fr auto minmax(30%, 1fr)); grid-template-rows: calc(4em - 5px) Additional examples of valid grid track definitions:

While grid lines can always be referred to by their numerical index, named lines can make the grid-placement properties easier to understand and maintain. Lines can be explicitly named in the grid-template-rows and grid-template-columns properties, or implicitly named by creating named grid areas with the grid-template-areas property.

<style> #grid { display: grid; grid-template-columns: [first nav] 150px [main] 1fr [last]; grid-template-rows: [first header] 50px [main] 1fr [footer] 50px [last]; } </style> Named Grid Lines. For example, the following code gives meaningful names to all of the lines in the grid. Note that some of the lines have multiple names.

5.1.2. Repeating Rows and Columns: the repeat() notation

The repeat() notation represents a repeated fragment of the track list, allowing a large number of columns or rows that exhibit a recurring pattern to be written in a more compact form. The syntax of the repeat() notation is:

The first argument specifies the number of repetitions. The second argument is a track list, which is repeated that number of times. The repeat() notation cannot be nested; doing so makes the declaration invalid.

<style> #grid { display: grid; grid-template-columns: 10px [col-start] 250px [col-end] 10px [col-start] 250px [col-end] 10px [col-start] 250px [col-end] 10px [col-start] 250px [col-end] 10px; grid-template-rows: 1fr; } /* Equivalent definition. */ #grid { display: grid; grid-template-columns: repeat(4, 10px [col-start] 250px [col-end]) 10px; grid-template-rows: 1fr; } </style> This example shows two equivalent ways of writing the same grid definition. Both ways produce a grid with a single row and four "main" columns, each 250px wide, surrounded by 10px "gutter" columns.

If the repeat() function ends up placing two <line-names> adjacent to each other, the name lists are merged. For example, repeat(2, [a] 1fr [b]) is equivalent to [a] 1fr [b a] 1fr [b].

We’re trying to solve this problem, which should be easy, but isn’t at the moment.

If the number of repetitions is auto and the grid container has a definite size or max size in the relevant axis, then the number of repetitions is the largest possible integer that does not cause the grid to overflow its grid container (treating all tracks as their max track sizing function if that is definite or as zero otherwise). Otherwise, the track list repeats only once. A <track-list> with more than one auto repeat() function, or with any content-sized tracks in addition to the auto repeat() function, is invalid.

François suggests a way to generate "just enough" repeated columns for the number of items in the grid. (see discussion) One proposal is to have two keywords instead of just one auto keyword: auto-fill to fill the grid with repetitions, and auto-fit to fill the grid and then drop empty repetitions.

5.1.3. Flexible Lengths: the fr unit

A flexible length or <flex> is a dimension with the fr unit, which represents a fraction of the free space in the grid container.

The distribution of free space occurs after all non-flexible track sizing functions have reached their maximum. The total size of such rows or columns is subtracted from the available space, yielding the free space, which is then divided among the flex-sized rows and columns in proportion to their flex factor.

Note: Flexible lengths in a track list work similarly to flexible lengths with a zero base size in [CSS3-FLEXBOX].

Each column or row’s share of the free space can be computed as the column or row’s <flex> * <free space> / <sum of all flex factors> . For the purpose of this calculation, a flexible length in the min position of a minmax() function is treated as 0 (an inflexible length).

When the available space is infinite (which happens when the grid container’s width or height is indefinite), flex-sized grid tracks are sized to their contents while retaining their respective proportions. The used size of each flex-sized grid track is computed by determining the max-content size of each flex-sized grid track and dividing that size by the respective flex factor to determine a “hypothetical 1fr size”. The maximum of those is used as the resolved 1fr length (the flex fraction ), which is then multiplied by each grid track’s flex factor to determine its final size.

A grid item can itself be a grid container by giving it display: grid; in this case the layout of its contents will be independent of the layout of the grid it participates in.

In some cases it might be necessary for the contents of multiple grid items to align to each other. A grid container that is itself a grid item can defer the definition of its rows or columns to its parent grid container by using the subgrid keyword in grid-template-rows and/or grid-template-columns, making it a subgrid in that dimension. In this case, the grid items of the subgrid participate in sizing the grid of the parent grid container, allowing the contents of both grids to align.

If a grid container that is not a grid item uses the subgrid keyword, its grid-template-rows/grid-template-columns value is treated identically to none (i.e. it doesn’t have an explicit grid in that dimension).

<ul> <li><label>Name:</label> <input name=fn> <li><label>Address:</label> <input name=address> <li><label>Phone:</label> <input name=phone> </ul> For example, suppose we have a form consisting of a list of inputs with labels: We want the labels and inputs to align, and we want to style each list item with a border. This can be accomplished with subgrid layout: ul { display: grid; grid-auto-flow: row; grid-template-columns: auto 1fr; } li { display: grid; grid: subgrid; margin: 0.5em; border: solid; padding: 0.5em; } label { grid-column: 1; } input { grid-column: 2; }

A subgrid behaves just like a normal grid container except that:

5.1.5. Resolved Values

When an element’s display is grid or inline-grid and it generates a box, the resolved value of the grid-template-rows and grid-template-columns properties is the used value, serialized as follows:

Every track listed, whether implicitly or explicitly created.

Every track size given as a length in pixels, regardless of sizing function.

A contiguous run of two or more tracks that have the same size and associated line names may be serialized with the repeat() notation.

Otherwise, (e.g. when the element has display: none or is not a grid) the resolved value is simply the computed value.

<style> #grid { width: 500px; grid-template-columns: [a] auto [b] minmax(min-content, 1fr) [b c d] repeat(2, [e] 40px) repeat(5, auto); } </style> <div id="grid"> <div style="grid-column-start:1; width:50px"></div> <div style="grid-column-start:9; width:50px"></div> </div> <script> var gridElement = document.getElementById("grid"); getComputedStyle(gridElement).gridTemplateColumns; // [a] 50px [b] 320px [b c d] repeat(2, [e] 40px) repeat(4, 0px) 50px </script>

Note: In general, resolved values are the computed values, except for a small list of legacy 2.1 properties. However, compatibility with early implementations of this module requires us to define grid-template-rows and grid-template-columns as returning used values. Authors are recommended to use the .rawComputedStyle and .usedStyle attributes instead of getComputedStyle() .

Name: grid-template-areas Value: none | <string>+ Initial: none Applies to: grid containers Inherited: no Percentages: n/a Media: visual Computed value: specified value Animatable: no

This property specifies named grid areas , which are not associated with any particular grid item, but can be referenced from the grid-placement properties. The syntax of the grid-template-areas property also provides a visualization of the structure of the grid, making the overall layout of the grid container easier to understand.

Values have the following meanings:

head ), navigational content ( nav ), footer content ( foot ), and main content ( main ). Accordingly, the template creates three rows and two columns, with four head area spans both columns and the first row of the grid. <style type="text/css"> #grid { display: grid; grid-template-areas: "head head" "nav main" "foot ...." } #grid > header { grid-area: head; } #grid > nav { grid-area: nav; } #grid > main { grid-area: main; } #grid > footer { grid-area: foot; } </style> In this example, the grid-template-areas property is used to create a page layout where areas are defined for header content (), navigational content (), footer content (), and main content (). Accordingly, the template creates three rows and two columns, with four named grid areas . Thearea spans both columns and the first row of the grid.

5.2.1. Implicit Named Lines

The grid-template-areas property creates implicit named lines from the named grid areas in the template. For each named grid area foo , four implicit named lines are created: two named foo-start, naming the row-start and column-start lines of the named grid area, and two named foo-end, naming the row-end and column-end lines of the named grid area.

These named lines behave just like any other named line, except that they do not appear in the value of grid-template-rows/grid-template-columns. Even if an explicit line of the same name is defined, the implicit named lines are just more lines with the same name.

5.2.2. Implicit Named Areas

Since a named grid area is referenced by the implicit named lines it produces, explicitly adding named lines of the same form (foo-start/foo-end) effectively creates a named grid area. Such implicit named areas do not appear in the value of grid-template-areas, but can still be referenced by the grid-placement properties.

5.3. Explicit Grid Shorthand: the grid-template property

The grid-template property is a shorthand for setting grid-template-columns, grid-template-rows, and grid-template-areas in a single declaration. It has several distinct syntax forms:

none Sets all three properties to their initial values (none). subgrid Sets grid-template-rows and grid-template-columns to subgrid, and grid-template-areas to its initial value. <‘grid-template-columns’> / <‘grid-template-rows’> Sets grid-template-columns and grid-template-rows to the specified values, respectively, and sets grid-template-areas to none. grid-template: auto 1fr auto / auto 1fr; is equivalent to grid-template-columns: auto 1fr auto; grid-template-rows: auto 1fr; grid-template-areas: none; [ <track-list> / ]? [ <line-names>? <string> <track-size>? <line-names>? ]+ Sets grid-template-columns to the track listing specified before the slash (or none, if not specified).

Sets grid-template-areas to the strings listed after the slash.

Sets grid-template-rows to the <track-size>s following each string (filling in auto for any missing sizes), and splicing in the named lines defined before/after each size. This syntax allows the author to align track names and sizes inline with their respective grid areas. grid-template: auto 1fr auto / [header-top] "a a a" [header-bottom] [main-top] "b b b" 1fr [main-bottom]; is equivalent to grid-template-columns: auto 1fr auto; grid-template-rows: [header-top] auto [header-bottom main-top] 1fr [main-bottom]; grid-template-areas: "a a a" "b b b";

Note: The grid shorthand accepts the same syntax, but also resets the implicit grid properties to their initial values. Unless authors want those to cascade in separately, it is therefore recommended to use grid instead of grid-template.

6. The Implicit Grid

The grid-template property and its longhands define a fixed number of tracks that form the explicit grid. When grid items are positioned outside of these bounds, the grid container generates implicit grid tracks by adding implicit grid lines to the grid. These lines together with the explicit grid form the implicit grid . The grid-auto-rows and grid-auto-columns properties size these implicit grid tracks.

The grid-auto-flow property controls auto-placement of grid items without an explicit position. Once the explicit grid is filled (or if there is no explicit grid) auto-placement will also cause the generation of implicit grid tracks.

6.1. Sizing Auto-generated Rows and Columns: the grid-auto-rows and grid-auto-columns properties

If a grid item is positioned into a row or column that is not explicitly sized by grid-template-rows or grid-template-columns, implicit grid tracks are created to hold it. This can happen either by explicitly positioning into a row or column that is out of range, or by the auto-placement algorithm creating additional rows or columns. The grid-auto-columns and grid-auto-rows properties specify the size of such implicitly-created tracks.

6.2. Automatic Placement : the : the grid-auto-flow property

Name: grid-auto-flow Value: [ row | column ] || dense Initial: row Applies to: grid containers Inherited: no Percentages: n/a Media: visual Computed value: specified value Animatable: no

Grid items that aren’t explicitly placed are automatically placed into an unoccupied space in the grid container by the auto-placement algorithm. grid-auto-flow controls how the auto-placement algorithm works, specifying exactly how auto-placed items get flowed into the grid. See §9.4 Grid Item Placement Algorithm for details on precisely how the auto-placement algorithm works.

row The auto-placement algorithm places items by filling each row in turn, adding new rows as necessary. If neither row nor column is provided, row is assumed. column The auto-placement algorithm places items by filling each column in turn, adding new columns as necessary. dense If specified, the auto-placement algorithm uses a “dense” packing algorithm, which attempts to fill in holes earlier in the grid if smaller items come up later. This may cause items to appear out-of-order, when doing so would fill in holes left by larger items. If omitted, a “sparse” algorithm is used, where the placement algorithm only ever moves “forward” in the grid when placing items, never backtracking to fill holes. This ensures that all of the auto-placed items appear “in order”, even if this leaves holes that could have been filled by later items.

Note: A future level of this module is expected to add a value that flows auto-positioned items together into a single “default” cell.

Auto-placement takes grid items in order-modified document order.

<style type="text/css"> form { display: grid; /* Define three columns, all content-sized, and name the corresponding lines. */ grid-template-columns: [labels] auto [controls] auto [oversized] auto; grid-auto-flow: row dense; } form > label { /* Place all labels in the "labels" column and automatically find the next available row. */ grid-column: labels; grid-row: auto; } form > input, form > select { /* Place all controls in the "controls" column and automatically find the next available row. */ grid-column: controls; grid-row: auto; } #department-block { /* Auto place this item in the "oversized" column in the first row where an area that spans three rows won’t overlap other explicitly placed items or areas or any items automatically placed prior to this area. */ grid-column: oversized; grid-row: span 3; } /* Place all the buttons of the form in the explicitly defined grid area. */ #buttons { grid-row: auto; /* Ensure the button area spans the entire grid element in the row axis. */ grid-column: 1 / -1; text-align: end; } </style> <form> <label for="firstname">First name:</label> <input type="text" id="firstname" name="firstname" /> <label for="lastname">Last name:</label> <input type="text" id="lastname" name="lastname" /> <label for="address">Address:</label> <input type="text" id="address" name="address" /> <label for="address2">Address 2:</label> <input type="text" id="address2" name="address2" /> <label for="city">City:</label> <input type="text" id="city" name="city" /> <label for="state">State:</label> <select type="text" id="state" name="state"> <option value="WA">Washington</option> </select> <label for="zip">Zip:</label> <input type="text" id="zip" name="zip" /> <div id="department-block"> <label for="department">Department:</label> <select id="department" name="department" multiple> <option value="finance">Finance</option> <option value="humanresources">Human Resources</option> <option value="marketing">Marketing</option> </select> </div> <div id="buttons"> <button id="cancel">Cancel</button> <button id="back">Back</button> <button id="next">Next</button> </div> </form> In the following example, there are three columns, each auto-sized to their contents. No rows are explicitly defined. The grid-auto-flow property is row which instructs the grid to search across its three columns starting with the first row, then the next, adding rows as needed until sufficient space is located to accommodate the position of any auto-placed grid item

7. Grid Definition Shorthand: the grid property

Name: grid Value: <‘grid-template’> | [ <‘grid-auto-flow’> [ <‘grid-auto-columns’> [ / <‘grid-auto-rows’> ]? ]? ] Initial: see individual properties Applies to: grid containers Inherited: see individual properties Percentages: see individual properties Media: visual Computed value: see individual properties Animatable: no

The grid property is a shorthand that sets all of the explicit grid properties (grid-template-rows, grid-template-columns, and grid-template-areas), all the implicit grid properties (grid-auto-rows, grid-auto-columns, and grid-auto-flow), and the gutter properties (column-gap and row-gap) in a single declaration. If <‘grid-auto-rows’> value is omitted, it is set to the value specified for grid-auto-columns. Other omitted values are set to their initial values.

Note: Note that you can only specify the explicit or the implicit grid properties in a single grid declaration. The sub-properties you don’t specify are set to their initial value, as normal for shorthands. Also, the gutter properties are reset by this shorthand, even though they can’t be set by it.

8. Clamping Overlarge Grids

Since memory is not infinite, UAs may clamp the the possible size of the grid to within a UA-defined limit, dropping all lines outside that limit. If a grid item is placed outside this limit, its grid area must be clamped to within this limited grid.

To clamp a grid area :

If the grid area would span outside the limited grid, its span is clamped to the last line of the limited grid.

If the grid area would be placed completely outside the limited grid is span must be truncated to 1 and the area repositioned into the last grid track on that side of the grid.

.grid-item { grid - row : 500 / 1500 ; grid - column : 2000 / 3000 ; } For example, if a UA only supported grids with at most 1000 tracks in each dimension, the following placement properties: Would end up being equivalent to: .grid-item { grid - row : 500 / 1000 ; grid - column : 999 / 1000 ; }

9. Placing Grid Items

Every grid item has a grid area, a rectangular set of grid cells that the grid item occupies. This grid area defines the containing block for the grid item within which the alignment properties (justify-self and align-self) determine their actual position. The cells that a grid item occupies also influence the sizing of the grid’s rows and columns, defined in §12 Grid Sizing.

The location of a grid item’s grid area within the grid is defined by its placement , which consists of a grid position and a grid span:

The grid-placement properties — the longhands grid-row-start, grid-row-end, grid-column-start, grid-column-end, and their shorthands grid-row, grid-column, and grid-area— allow the author to specify a grid item’s placement by providing any (or none) of the following six pieces of information:

Row Column Start row-start line column-start line End row-end line column-end line Span row span column span

A definite value for any two of Start , End , and Span in a given dimension implies a definite value for the third.

The following table summarizes the conditions under which a grid position or span is definite or automatic:

Position Span Definite At least one specified line Explicit, implicit, or defaulted span.

Note: Non- subgrids default to 1. Automatic No lines explicitly specified Subgrid without an explicit or implied span

9.1. Common Patterns for Grid Placement

This section is informative.

The grid-placement property longhands are organized into three shorthands:

9.1.1. Named Areas

An item can be placed into a named grid area (such as those produced by the template in grid-template-areas) by specifying the area’s name in grid-area:

article { grid-area: main; /* Places item into the named area "main". */ }

An item can also be partially aligned with a named grid area, with other edges aligned to some other line:

.one { grid-row-start: main; /* Align the row-start edge to the start edge of the "main" named area. */ }

9.1.2. Numeric Indexes and Spans

Grid items can be positioned and sized by number, which is particularly helpful for script-driven layouts:

.two { grid-row: 2; /* Place item in the second row. */ grid-column: 3; /* Place item in the third column. */ /* Equivalent to grid-area: 2 / 3; }

By default, a grid item has a span of 1. Different spans can be given explicitly:

.three { grid-row: 2 / span 5; /* Starts in the 2nd row, spans 5 rows down (ending in the 7th row). */ } .four { grid-row: span 5 / 7; /* Ends in the 7th row, spans 5 rows up (starting in the 2nd row). */ }

Note: Note that grid indexes are writing mode relative. For example, in a right-to-left language like Arabic, the first column is the rightmost column.

9.1.3. Named Lines and Spans

Instead of counting lines by number, named lines can be referenced by their name:

.five { grid-column: first / middle; /* Span from line "first" to line "middle". */ }

Note: Note that if a named grid area and a named line have the same name, the placement algorithm will prefer to use named grid area’s edge instead.

If there are multiple lines of the same name, they effectively establish a named set of grid lines, which can be exclusively indexed by filtering the placement by name:

.six { grid-row: text 5 / text 7; /* Span between the 5th and 7th lines named "text". */ grid-row: text 5 / span text 2; /* Same as above. */ }

9.1.4. Auto Placement

A grid item can be automatically placed into the next available empty grid cell, growing the grid if there’s no space left.

.eight { grid-area: auto; /* Initial value */ }

This can be used, for example, to list a number of sale items on a catalog site in a grid pattern.

Auto-placement can be combined with an explicit span, if the item should take up more than one cell:

.nine { grid-area: span 2 / span 3; /* Auto-placed item, covering two rows and three columns. */ }

Whether the auto-placement algorithm searchs across and adds rows, or searches across and adds columns, is controlled by the grid-auto-flow property.

Note: By default, the auto-placement algorithm looks linearly through the grid without backtracking; if it has to skip some empty spaces to place a larger item, it will not return to fill those spaces. To change this behavior, specify the dense keyword in grid-auto-flow.

9.1.5. Auto Sizing Subgrids

A subgrid without a definite grid span is sized to its implicit grid, i.e. all of its items within it are first placed into its own grid, and its span is the resulting size of its grid.

.adverts { grid: subgrid; grid-column: span 2; } For example, a subgrid spanning two columns can be given an auto-spanning block size If it contains 10 auto-placed items, it will span 5 rows in its parent grid.

Note: Since auto-spanning subgrids determine their span before being positioned, they can also be auto-positioned. The above example would auto-place the .adverts block, if no further rules specified its position.

The grid-row-start, grid-column-start, grid-row-end, and grid-column-end properties determine a grid item’s size and location within the grid by contributing a line, a span, or nothing (automatic) to its grid placement, thereby specifying the inline-start, block-start, inline-end, and block-end edges of its grid area.

Values have the following meanings:

1 2 3 4 5 6 7 8 9 +--+--+--+--+--+--+--+--+ | | | | | | | | | A B C A B C A B C | | | | | | | | | +--+--+--+--+--+--+--+--+ Given a single-row, 8-column grid and the following 9 named lines: The following declarations place the grid item between the lines indicated by index: grid-column-start: 4; grid-column-end: auto; /* Line 4 to line 5 */ grid-column-start: auto; grid-column-end: 6; /* Line 5 to line 6 */ grid-column-start: C; grid-column-end: C -1; /* Line 3 to line 9 */ grid-column-start: C; grid-column-end: span C; /* Line 3 to line 6 */ grid-column-start: span C; grid-column-end: C -1; /* Line 6 to line 9 */ grid-column-start: span C; grid-column-end: span C; /* Error: The end span is ignored, and an auto-placed item can’t span to a named line. Equivalent to grid-column: span 1;. */ grid-column-start: 5; grid-column-end: C -1; /* Line 5 to line 9 */ grid-column-start: 5; grid-column-end: span C; /* Line 5 to line 6 */ grid-column-start: 8; grid-column-end: 8; /* Error: line 8 to line 9 */ grid-column-start: B 2; grid-column-end: span 1; /* Line 5 to line 6 */

9.2.1. Grid Placement Conflict Handling

If the placement for a grid item contains two lines, and the start line is further end-ward than the end line, swap the two lines.

If the placement contains two spans, remove the one contributed by the end grid-placement property.

If the placement contains only a span for a named line, replace it with a span of 1.

Name: grid-row , grid-column Value: <grid-line> [ / <grid-line> ]? Initial: see individual properties Applies to: grid items and absolutely-positioned boxes whose containing block is a grid container Inherited: see individual properties Percentages: see individual properties Media: visual Computed value: see individual properties Animatable: no

The grid-row and grid-column properties are shorthands for grid-row-start/grid-row-end and grid-column-start/grid-column-end, respectively.

If two <grid-line> values are specified, the grid-row-start/grid-column-start longhand is set to the value before the slash, and the grid-row-end/grid-column-end longhand is set to the value after the slash.

When the second value is omitted, if the first value is a <custom-ident>, the grid-row-end/grid-column-end longhand is also set to that <custom-ident>; otherwise, it is set to auto.

Name: grid-area Value: <grid-line> [ / <grid-line> ]{0,3} Initial: see individual properties Applies to: grid items and absolutely-positioned boxes whose containing block is a grid container Inherited: see individual properties Percentages: see individual properties Media: visual Computed value: see individual properties Animatable: no

If four <grid-line> values are specified, grid-row-start is set to the first value, grid-column-start is set to the second value, grid-row-end is set to the third value, and grid-column-end is set to the fourth value.

When grid-column-end is omitted, if grid-column-start is a <custom-ident>, grid-column-end is set to that <custom-ident>; otherwise, it is set to auto.

When grid-row-end is omitted, if grid-row-start is a <custom-ident>, grid-row-end is set to that <custom-ident>; otherwise, it is set to auto.

When grid-column-start is omitted, if grid-row-start is a <custom-ident>, all four longhands are set to that value. Otherwise, it is set to auto.

Note: The resolution order for this shorthand is row-start/column-start/row-end/column-end, which goes CCW for LTR pages, the opposite direction of the related 4-edge properties using physical directions, like margin.

9.4. Grid Item Placement Algorithm

The following grid item placement algorithm resolves automatic positions of grid items into definite positions, ensuring that every grid item has a well-defined grid area to lay out into. (Grid spans need no special resolution; if they’re not explicitly specified, they default to either 1 or, for subgrids, the size of their explicit grid.)

Note: This algorithm can result in the creation of new rows or columns in the implicit grid, if there is no room in the explicit grid to place an auto-positioned grid item.

Every grid cell (in both the explicit and implicit grids) can be occupied or unoccupied . A cell is occupied if it’s covered by a named grid area, or by the grid area of a grid item with a definite grid position; otherwise, the cell is unoccupied. A cell’s occupied/unoccupied status can change during this algorithm.

To aid in clarity, this algorithm is written with the assumption that grid-auto-flow has row specified. If it is instead set to column, swap all mentions of rows and columns, inline and block, etc. in this algorithm.

10. Absolute Positioning

10.1. With a Grid Container as Containing Block

If an absolutely positioned element’s containing block is generated by a grid container, the containing block corresponds to the grid area determined by its grid-placement properties. The offset properties (top/right/bottom/left) then indicate offsets inwards from the corresponding edges of this containing block, as normal.

Note: While absolutely-positioning an element to a grid container does allow it to align to that container’s grid lines, such elements do not take up space or otherwise participate in the layout of the grid.

.grid { grid: 10rem 10rem 10rem 10rem / 1fr 1fr 1fr 1fr; /* 4 columns of 10rem each, 4 equal-height rows filling the grid container */ justify-content: center; /* center the grid horizontally within the grid container */ position: relative; /* Establish abspos containing block */ } .abspos { grid-row-start: 1; /* 1st grid row line = top of grid container */ grid-row-end: span 2; /* 3rd grid row line */ grid-column-start: 3; /* 3rd grid col line */ grid-column-end: auto; /* right padding edge */ /* Containing block covers the top right quadrant of the grid container */ position: absolute; top: 70px; bottom: 40px; left: 100px; right: 30px; } Note: Grids and the grid-placement properties are flow-relative, while abspos offsets are physical, so if the direction or writing-mode properties change, the grid will transform to match, but the offsets won’t.

Instead of auto-placement, an auto value for a grid-placement property contributes a special line to the placement whose position is that of the corresponding padding edge of the grid container (the padding edge of the scrollable area, if the grid container overflows). These lines become the first and last lines (0th and -0th) of the augmented grid used for positioning absolutely-positioned items.

Note: Thus, by default, the absolutely-positioned box’s containing block will correspond to the padding edges of the grid container, as it does for block containers.

Absolute positioning occurs after layout of the grid and its in-flow contents and does not contribute to the sizing of any grid tracks or affect the size/configuration of the grid in any way. If a grid-placement property refers to a non-existent line either by explicitly specifying such a line or by spanning outside of the existing implicit grid, it is instead treated as specifying auto (instead of creating new implicit grid lines).

If the placement only contains a grid span, replace it with the two auto lines in that axis. (This happens when both grid-placement properties in an axis contributed a span originally, and §9.2.1 Grid Placement Conflict Handling caused the second span to be ignored.)

10.2. With a Grid Container as Parent

The static position [CSS21] of an absolutely-positioned child of a grid container is determined as if it were the sole grid item in a grid area whose edges coincide with the padding edges of the grid container. However, if the grid container parent is also the generator of the absolutely positioned element’s containing block, instead use the grid area determined in §10.1 With a Grid Container as Containing Block.

Note: Note that this position is affected by the values of justify-self and align-self on the child, and that, as in most other layout models, the absolutely-positioned child has no effect on the size of the containing block or layout of its contents.

11. Alignment and Spacing

After a grid container’s grid tracks have been sized, and the dimensions of all grid items are finalized, grid items can be aligned within their grid areas.

The margin properties can be used to align items in a manner similar to, but more powerful than, what margins can do in block layout. Grid items also respect the alignment properties from the Box Alignment spec, which allow easy keyword-based alignment of items in both the row axis and column axis.

By default, grid items stretch to fill their grid area. However, if justify-self or align-self compute to a value other than stretch or margins are auto, grid items will auto-size to fit their contents.

Name: row-gap , column-gap Value: normal | <length> Initial: normal Applies to: grid containers Inherited: no Percentages: n/a Media: visual Computed value: specified value Animatable: no

These properties specify the gutters between grid rows and grid columns, respectively. The effect is as though the affected grid lines acquired width: the grid track between two grid lines is the space between the gutters that represent them. For the purpose of track sizing, each gutter is essentially treated as an extra track of the specified length.

Note: Additional spacing may be added between tracks due to justify-content/align-content. See §12.1 Grid Sizing Algorithm. This space effectively increases the size of the gutters.

On grid containers, a value of normal computes to zero.

Should we have grid-specific properties for this (e.g. grid-row-gap) instead of sharing with multicol (row-gap)? Sharing with multi-col could be problematic if we re-use the grid-template properties to set up grid-snapping.

This property is a shorthand that sets column-gap and row-gap in one declaration. If <‘row-gap’> is omitted, it’s set to the same value as <‘column-gap’>.

11.2. Aligning with auto margins

This section is non-normative. The normative definition of how margins affect grid items is in §12 Grid Sizing.

Auto margins on grid items have an effect very similar to auto margins in block flow:

During calculations of grid track sizes, auto margins are treated as 0 .

. Auto margins absorb positive free space prior to alignment via the alignment properties (defined in the next sections).

Overflowing elements ignore their auto margins and overflow in the end directions.

Note: Note that, if free space is distributed to auto margins, the alignment properties will have no effect in that dimension because the margins will have stolen all the free space left over after sizing.

TODO: EXAMPLE HERE

Grid items can be aligned in the inline dimension by using the justify-self property on the grid item or justify-items property on the grid container, as defined in [CSS3-ALIGN].

Grid items can also be aligned in the block dimension (perpendicular to the inline dimension) by using the align-self property on the grid item or align-items property on the grid container, as defined in [CSS3-ALIGN].

If the grid’s outer edges do not correspond to the grid container’s content edges (for example, if no columns are flex-sized), the grid tracks are aligned within the content box according to the justify-content and align-content properties on the grid container.

.grid { display: grid; grid: 12rem 12rem 12rem 12rem / 10rem 10rem 10rem 10rem; justify-content: end; align-content: center; } For example, the following grid is centered vertically, and aligned to the right edge of its grid container

Note that certain values of justify-content and align-content can cause the tracks to be spaced apart (space-around, space-between, space-evenly) or to be resized (stretch).

The stretch value only affects auto-sized tracks at the moment. Should it instead affect all tracks?

11.6. Grid Baselines

The baselines of a grid container are determined as follows:

A grid item participates in baseline alignment in a particular dimension if its value for align-self or justify-self, as appropriate, is baseline and its inline axis is parallel to that dimension.

order-modified grid order is the order in which grid items are encountered when traversing the grid’s grid cells, in row-major order if calculating the inline-axis baseline, or in column-major order if calculating the block-axis baseline. If two items are encountered at the same time, they are taken in order-modified document order.

When calculating the baseline according to the above rules, if the box contributing a baseline has an overflow value that allows scrolling, the box must be treated as being in its initial scroll position for the purpose of determining its baseline.

When determining the baseline of a table cell, a grid container provides a baseline just as a line box or table-row does. [CSS21]

12. Grid Sizing

This section defines the grid sizing algorithm , which determines the size of all grid tracks and, by extension, the entire grid.

Each track has specified minimum and maximum sizing functions (which may be the same). Each sizing function is either:

A fixed sizing function (<length> or resolveable <percentage>).

(<length> or resolveable <percentage>). An intrinsic sizing function (min-content, max-content, or auto).

(min-content, max-content, or auto). A flexible sizing function (<flex>).

The grid sizing algorithm defines how to resolve these sizing constraints into used track sizes.

12.1. Grid Sizing Algorithm

Once the size of each grid area is thus established, the grid items are laid out into their respective containing blocks.

12.2. Track Sizing Terminology

12.3. Track Sizing Algorithm

The remainder of this section is the track sizing algorithm , which calculates from the min and max track sizing functions the used track size. Each track has a base size , a <length> which grows throughout the algorithm and which will eventually be the track’s final size, and a growth limit , a <length> which provides a desired maximum size for the base size. There are 4 steps:

12.4. Initialize Track Sizes

Initialize each track’s base size and growth limit. For each track, if the track’s min track sizing function is:

For each track, if the track’s max track sizing function is:

In all cases, if the growth limit is less than the base size, increase the growth limit to match the base size.

Note: Gutters are treated as fixed-size tracks for the purpose of the track sizing algorithm.

12.5. Resolve Intrinsic Track Sizes

This step resolves intrinsic track sizing functions to absolute lengths. First it resolves those sizes based on items that are contained wholly within a single track. Then it gradually adds in the space requirements of items that span multiple tracks, evenly distributing the extra space across those tracks insofar as possible.

When the grid container is being sized under a min-content constraint, a track with a flexible min track sizing function is treated as if its min track sizing function was min-content for the purposes of this step. This seems correct, but should be checked because it wasn’t in the original algorithm.

Note: There is no single way to satisfy these constraints when items span across multiple tracks. This algorithm embodies a number of heuristics which have been seen to deliver good results on real-world use-cases, such as the "game" examples earlier in this specification. This algorithm may be updated in the future to take into account more advanced heuristics as they are identified.

To distribute extra space by increasing the affected sizes of a set of tracks as required by a set of intrinsic size contributions,

Note: When this step is complete, all intrinsic base sizes and growth limits will have been resolved to absolute lengths.

12.6. Maximize Tracks

If the free space is positive, distribute it equally to all tracks, freezing tracks as they reach their growth limits (and continuing to grow the unfrozen tracks as needed).

For the purpose of this step: if sizing the grid container under a max-content constraint, the free space is infinite; if sizing under a min-content constraint, the free space is zero.

12.7. Stretch Flexible Tracks

This step sizes flexible tracks using the largest value it can assign to an fr without exceeding the available space.

First, find the used flex fraction:

For each flexible track, if the product of the used flex fraction and the track’s flex factor is greater than the track’s base size, set its base size to that product.

12.7.1. Find the Size of an fr

This algorithm finds the largest size that an fr unit can be without exceeding the target size. It must be called with a set of grid tracks and some quantity of space to fill .

13. Fragmenting Grid Layout

Grid containers can break across pages between rows and inside items. The break-* properties apply to grid containers as normal for the formatting context in which they participate. This section defines how they apply to grid items and the contents of grid items.

The following breaking rules refer to the fragmentation container as the “page”. The same rules apply to any other fragmentation containers. (Substitute “page” with the appropriate fragmentation container type as needed.) See the CSS3 Fragmentation Module [CSS3-BREAK].

The exact layout of a fragmented grid container is not defined in this level of Grid Layout. However, breaks inside a grid container are subject to the following rules:

The break-before and break-after properties on flex items are propagated to their grid row. The break-before property on the first row and the break-after property on the last row are propagated to the grid container.

A forced break inside a grid item effectively increases the size of its contents; it does not trigger a forced break inside sibling items.

Class A break opportunities occur between rows, and Class C break opportunities occur between the first/last row and the flex container’s content edges. [CSS3-BREAK]

When a grid container is continued after a break, the space available to its grid items (in the block flow direction of the fragmentation context) is reduced by the space consumed by grid container fragments on previous pages. The space consumed by a grid container fragment is the size of its content box on that page. If as a result of this adjustment the available space becomes negative, it is set to zero.

Aside from the rearrangement of items imposed by the previous point, UAs should attempt to minimize distortation of the grid container with respect to unfragmented flow.

13.1. Sample Fragmentation Algorithm

This is just a rough draft. This section needs to be severely cross-checked with the [CSS3-FLEXBOX] algorithm. Feedback overall is welcome; please reference the rules above instead as implementation guidance.

Layout the grid following the §12 Grid Sizing by using the fragmentainer box width and assume unlimited height. During this step all grid-row auto and fr values must be resolved. Layout the grid container using the values resolved in the previous step. If a grid area dimensions change due to fragmentation (do not include items that span rows in this decision), increase the grid row as necessary for rows that either: have a content min track sizing function.

are in a grid that does not have an explicit height and the grid row is flexible. If the grid height is auto, the height of the grid should be the sum of the final row sizes. If a grid area overflows the grid container due to margins being collapsed during fragmentation, extend the grid container to contain this grid area (this step is necessary in order to avoid circular layout dependencies due to fragmentation).

If the grid’s height is specified, steps three and four may cause the grid rows to overflow the grid.

Acknowledgements

This specification is made possible by input from Erik Anderson, Rossen Atanassov, Manuel Rego Casasnovas, Arron Eicholz, Sylvain Galineau, Markus Mielke, Daniel Holbert, John Jansen, Chris Jones, Kathy Kam, Veljko Miljanic, Mats Palmgren, François Remy, Peter Salas, Sergio Villar Senin, Christian Stockwell, Eugene Veselov, and the CSS Working Group members. Thanks also to Eliot Graff for editorial input.

Changes

The following significant changes were made since the 17 March 2015 Working Draft.

A Disposition of Comments is available.

Appendix A: Translated Layout Algorithm

Note: The following is a more direct translation of the original Microsoft editors' track sizing algorithm, from which the current algorithm is derived. It follows the original algorithm structure without being as programmatic in its language. It is preserved here to aid in review of the current specification (and will be removed in the next revision).

This algorithm is run multiple times, once for each set of grid items with a particular span count, and each time it moves through four phases, each one addressing one combination of min-content or max-content as a min track sizing function or max track sizing function.

Starting from the set of all grid items in the grid, remove any with a span count greater than one which span a track with a <flex> max track sizing function. Of the remaining, sort them into groups according to their span count, and order the groups in ascending order of span count. For each group, in order, perform the following steps four times: