Dark/Light theme default support

Offering light and dark modes, typically based on OS preferences through prefers-color-scheme, isn’t only a nice feature: it is an accessibility feature.

It seems to me that WordPress default themes should integrate that. It also means adapting the theme customization tools accordingly. (It would also provide a good example for theme devs.)

Additionally, it would be good to further upgrade the images handling and update the Image block in order to support user-theme-dependent images. Let’s say your article include some graph that uses a black text and transparent background. It looks great with your bright theme, but is unreadable with the dark theme used when the reader has their OS in dark mode. You should be able to set an alternative picture for the dark mode.

(Ideally, you should also be able to add dark-mode-only CSS kinda everywhere.)

Note: I might and up trying to implement a plugin that would (poorly) handle the alternate-image aspect of things. “Poorly” because it should probably be dealt with not within the image block, but in the media library. I’m probably not knowledgeable enough to efficiently work on both the media library and the theme customization controls.