> For example, in Firefox, I use the dark theme for the UI, but that’s completely unrelated to the content, and prefers-color-scheme matches the content, not the chrome. Content I keep normal, light.
I prefer this because now rather than setting dark mode to each site I go to, they can be signalled this already. There's no user friendly way to set firefox's prefer-color-scheme: dark if the OS does not have the capabilities to do that.
Yeah, I’ve been waiting for that to inevitably happen so that I can revert it. Speaking overly broadly, dark mode everything is normally an at-least-slightly bad idea, but there’s good cause for aesthetic (low-contrast) dark mode of chrome in order to get it mostly out of the way, so that you can focus on the content. This is essentially what most graphics programs default to nowadays, and the same reasoning can be applied to browsers. (Though it only really works if your windows are maximised, otherwise dark between two lights could become a distraction.) No one says “you have a dark desktop background, you must want everything on your system to be dark”. Comment 47’s “When using the "Dark" theme, "prefers-color-scheme" should be dark, because that's what the user requested.” is simply not right. Choosing a dark browser theme is honestly quite a weak hint about whether you want content to be dark. The conflation of this that recent forays into OS-wide dark modes has encouraged is not good.
> There's no user friendly way to set firefox's prefer-color-scheme: dark if the OS does not have the capabilities to do that.
And even if the OS does have that capability, Firefox will ignore it for prefers-color-scheme if you have enabled enhanced tracking protection. Instead, Firefox will always claim prefers-color-scheme: light - the least they could have done is indicate no preference.
The only reason its not useful is because browsers did not implement it or removed their implementation. There is even one use in my comment: specifying not providing false information when the browser does not want to disclose any more identifying bits.
Of note is https://bugzilla.mozilla.org/show_bug.cgi?id=1529323 which is requesting to change this behaviour to align prefers-color-scheme to the UI theme if there is no overriding behaviour.
I prefer this because now rather than setting dark mode to each site I go to, they can be signalled this already. There's no user friendly way to set firefox's prefer-color-scheme: dark if the OS does not have the capabilities to do that.