Feature request: CSS injection for dark theme

[Agvantibo]

It would be great if it were possible to adapt the codebase of something akin to https://github.com/darkreader/darkreader to restyle websites according to the OS GTK4 theme variant. This is probably way too labor-intensive, but a simple way to add css overrides would be very welcome, and provide a good starting point