Scope CSS to the preview

[sonnyp]

The CSS currently applies to the whole window so something like label { color: blue; } will leak outside the preview and into the application controls.

As pointed out in 2e02792 a solution would simply be to prefix all selectors with an id so that everything is scoped to the preview.

With a proper css ast-like parser and serializer it should be straightforward

• https://github.com/csstree/csstree (looks best)
• https://github.com/cwdoh/cssparser.js
• https://github.com/reworkcss/css
• https://github.com/postcss/postcss

cool explorer for css ast solutions https://astexplorer.net/

[sonnyp]

https://docs.gtk.org/gtk4/css-overview.html

we might not need a parser