Some UIs require rendering a light button in some places, but dark in another. It'd be nice if you could switch between these by using color-scheme, like you can with native widgets. However, right now there's no way to do this other than exclusively using system colors.

Chromium has -internal-light-dark(<light-color>, <dark-color>) for this. However color-scheme was designed a bit more generically than light / dark, so maybe we need a schemed-color(<custom-ident> <color>, <fallback-color>) or so, where the <custom-ident> is the scheme name, and the <color> is the color for that scheme. So -internal-light-dark(red, blue) would become schemed-color(light red, blue) or so.

This would allow authors to create widgets that properly react to color-scheme.