Simplify the theme selector menu

[brodieavoult]

Is your feature request related to a problem? Please describe.

I personally feel like the way that the theme selector in the Desktop site is split into two sections (?) is a little unnecessary and makes it feels a little clunky, and should be simplified.

Describe the solution you'd like

I've made a little mock-up to show how it could be improved upon. Maybe this isn't a perfect solution, but it's better than how it is currently.

[mary-ext]

Which dark theme variant should it use if you've set it to System?

[brodieavoult]

I don't see how that sort of behavior would be changed by my suggestion, so I suppose it would just behave the same as it does currently (Light for Light mode, and Dim for Dark mode). This is purely just an UX change.

[mary-ext]

Seems unclear to me though how that'd be the case? Unless you intend for it to be like so:

System mode should still let you change between Dim and Dark, hence why they're separate.