Ubuntu uses a custom libadwaita theme that matches more closely with the Yaru theme than the default libadwaita theme (e.g. orange accent color). This applies to Snap and native Deb-installed applications, but not to Flatpaks.
A solution for this was to use Gradience, but Gradience is currently unmaintained (although still works), so I am looking for a more future-proof solution. To the best of my knowledge, all gradience did was that it made an appropriate gtk.css file in ~/.config/gtk-4.0, (but maybe it also set some environment variables, I don't know, but didn't really see it in the source code). If flatpaks have access to this directory, they will use the set gtk4/libadwaita theme.
I have also tried to use the solution in https://askubuntu.com/a/1420996/658896, but letting flatpaks access the Yaru-dark theme while setting GTK-THEME=Yaru-dark will break libadwaita apps.
I have also tried to manually copy the contents of /usr/share/themes/Yaru-dark/gtk-4.0 to ~/.config/gtk-4.0, while flatpaks have access to this folder, but it had no effect on libadwaita flatpaks.
So then the questions are:
- Obviously, Ubuntu uses a nonstandard libadwaita style. Where is this located?
- Is there any known working practice of applying this to flatpaks, presumably by copying the style sheet somewhere (e.g. ~/.config/gtk-4.0) the flatpak apps have access to?
