Enhanced themes with custom CSS

[mindplay-dk]

I just discovered this very cool feature in Thorium:

Enable Native UI Inspection in DevTools chrome://flags Patch - Made by me.

Vivaldi has a similar feature, which I recently used to customize the UI in Vivaldi:

https://forum.vivaldi.net/topic/99504/perfecting-the-title-and-toolbar-design?_=1727779826238

Vivaldi additionally has a hidden feature that lets you customize the CSS:

https://gabevilela.vivaldi.net/2020/12/26/guide-customizing-vivaldis-ui-with-css-mods/

Does Thorium have anything like this? Or what's the use of the native UI inspection feature?

Also, as I wrote in that forum thread:

why isn't this feature built into Themes instead?

Even just a simple "css" string property in the theme file would go a long way.

Themes, as they are, is a rather bland and uninteresting feature - there is not much value in even switching themes in the first place, they are all more or less the same, just some colors and a background.

Adding custom CSS to themes would surely take this to the next level. 😄

Themes in Chrome based browsers generally can't do much - they change a few colors, that's about it.

Imagine opening up the whole UI for the community to customize - this could be a game changer, since pretty much anyone's favorite browser UI could be implemented as just a theme. For one, vertical tabs could be something a third party just offers in a theme.

As far as I know, this is not a feature any other browser has? 😄