No offense but how about bothering to finish Alternative Style Sheet selection?

   <link href="css.css" rel="stylesheet" title="Default Style" />
   <link href="a.css" rel="alternate stylesheet" title="light" />
   <link href="b.css" rel="alternate stylesheet" title="dark" />

https://html.spec.whatwg.org/multipage/links.html#rel-altern...

edit: with finish I mean use this for light/dark mode and fix it so that the preference chosen by the user is not immediately discarded after navigation. One doesn't discard user selected preferences. It is not done.

What if, in the future, we have more than two options (light and dark)?

@media (prefers-color-scheme: [name]) seems more extensible, but this feels simpler and easier to read.

Glad the function accepts custom properties (CSS "variables").

Should probably add a color property that doesn't use this function as a fallback for browsers that don't support it.

I think `black` and `white` should be switched here:

color: light-dark(black, white);