I actually like `light-dark`. It's a shortcut to something that can be done more comprehensively with other, longer forms, but tailored to the most common (by far!) use case. It's a wart in the spec (specific color schemes as keywords) so that we can remove the warts in our code (media query blocks in CSS).

It's not like CSS was pure and elegant to begin with, so why not add an oddity that is actually useful?