Try this:

defaults write -g NSRequiresAquaSystemAppearance -bool Yes

Then logout or restart. Then go to the system preferences and select dark mode. It will make top bar and dock dark while everything else in light mode.

To revert it back:

defaults write -g NSRequiresAquaSystemAppearance -bool No

EDIT: Please also have a look on the answers bellow, they are needed in order to make other parts working, like notification center & spotlight. Run all of the commands, and then logout. Still missing the trash can color :)