Document using -symbolic icons

[danirabbit]

Problem

I've seen a couple times developers including gresourced icons in dark and light variants instead of using the -symbolic namespace. We don't current document this so it's not obvious that this is a built-in feature

Proposal

Document:

• using -symbolic namespace for automatic dark/light icons
• coloring -symbolic icons using .accent in Gtk.CSS
• coloring -symbolic icons using semantic colors like error or success
• coloring .accent icons using named colors like red or green

Prior Art (Optional)

No response

[Antolius]

Could this be solved by expanding the Icon Browser app with preview of error / accented symbolic icons? If we had that docs could just mention the option and direct the reader to check live examples in the app, instead of explaining everything with text.

[danirabbit]

I think expanding the icon browser as an interactive example is good but I think we still need to document how developers can create and ship their own custom symbolic icons in addition to using the provided system ones