Yes, you can, and it doesn’t really matter in what order. A CSS preprocessor is not required. It works in regular CSS.

This works:

@supports(--a: b) { @media (min-width: 1px) { body { background: red; } } }

And so does this, the reverse nesting of the above:

@media (min-width: 1px) { @supports(--a: b) { body { background: green; } } }

You can keep going with the nesting, if it ever makes sense:

@media (min-width: 2px) { @media (min-width: 1px) { @supports (--a: b) { @supports (display: flex) { body { background: pink; } } } } }

There is probably a point where the logic of that gets out of hand, so careful. But hey, it works. Presumably, you can “infinitely” nest at-rules.

To look at nested code like that looks a little like a CSS preprocessor is in use, but that’s not the case here. Regular ol’ CSS handles this just fine, and in fact, CSS preprocessors don’t meaningfully manipulate it at all (tested Sass, Less, and Stylus).