Feature request: Advanced theming options

[leb-kuchen]

Theme Builder

Cosmic theme provides rich theming support, of which only a subset is covered by the appearance settings.

Values like warning, success and destructive are just colors and should be easy to change.
Generally I think we should provide all available options, though this would enable unreadable themes.

[ryanabx]

It'd be good to have theme error checking, but that's an extension to this feature

[leb-kuchen]

You mean checking the contrast?