Postponed from #12341... actually I'm not completely sure what to do here, might take some research.

Note users can already use SVG with CSS <style /> to achieve light and dark favicon, this would be useful for bitmap and for those who don't want to edit their SVG.

Previously:

Favicons ... It might make more sense to use the prefers-color-scheme media query for favicons because they’re outside the page and should follow system preferences.