Update dark mode guidance

[jannuary]

It has been obsolete since libadwaita anyway, but it is even more obsolete now with color scheme preference.

[xou816]

I have not had the chance to try out just yet! Curious to see how it works. If the system preference is set to dark or light, what does our PreferLight or PreferDark setting do exactly? Are we right to use these values?

[jannuary]

If the system preference is set to dark or light, what does our PreferLight or PreferDark setting do exactly?

System preference has three options: "Light" (not exposed in elementary or GNOME afaik), "Default" and "Dark".

With prefers-dark-mode on, "Default" or "Dark" = dark, "Light" = light;
with it off, "Light" and "Default" = light, "Dark" = dark.

Also see Alexander's blog post

Having PreferLight/PreferDark isn't ideal, but when we have an actual preferences window, we could have a System/Light/Dark tri-state toggle that maps to PreferLight/ForceLight/ForceDark

[xou816]

We could make it a tristate thing already, or just have Default (ie system preference) vs PrefersDark in the meantime!

[jannuary]

It could be yeah, though that also wouldn't make sense on systems without color scheme prefence.

Also, there is no "Default" from our side, just Prefer/Force Light or Dark