Feature request: Allow custom CSS overrides on top of existing themes

[arnofly]

Hi,

Currently the extension offers two options:

• Use one of the built-in themes
• Use a fully custom theme (limited to 8KB)

The 8KB limit combined with the all-or-nothing approach makes the custom theme option barely usable in practice.

It would be great to have a third option: a small "Custom CSS overrides" field where you can add a few rules that are injected on top of the selected theme, without replacing it entirely.

This would cover the most common use case: "I like the GitHub theme, I just want to tweak a couple of things."

Thx