It works on most websites, but sometimes it doesn't quite. Only have two gripes with it:

* doesn't detect if site is already using a dark mode. This would probably be a bit hard to implement, though, and is not the reason I've docked a star.
* there's some weird stuff going on with Twitch. It sometimes blacks out half the video even if twitch is "whitelisted" (which confusingly means "prevent extension from working on this site," as opposed to the standard "allow this"). Workaround for that is disabling overlays (e.g. dynamic follow buttons and amazon overlay).