AHAH!
`export GTK_THEME=theme-name` in your .bashrc file and suddenly #GTK4 behaves itself!
This is MUCH better than the slightly odd and patchy behaviour that I was getting from `.config/gtk-4.0/gtk.css`
Client Info
Server: https://mastodon.social
Version: 2025.07
Repository: https://github.com/cyevgeniy/lmst