Set a name on the fullscreen window, and require it in all selectors in the custom CSS. Fixes style leaking to other g-c-c bits. https://gitlab.gnome.org/GNOME/gnome-control-center/issues/504
Same dog, different collar. The UI has been ported 1:1 to GTK+, using GtkBuilder, CSS and event controllers fairly reduced the amount of code needed for this. It also allows us to stop initializing clutter-gtk across the several executables.