Thunar ignores GTK_THEME=Adwaita:dark and % cat .config/gtk-3.0/settings.ini [Settings] gtk-application-prefer-dark-theme = true while thunar-settings is dark with one of this setting.
I'm seeing similar issues. Using lxappearance or the lxde/xfce desktop tool to change the theme has no affect on Thunar's appearance. Checking both .gtkrc-2.0 and .config/gtk-3.0/settings.ini shows that the them is set correctly.
properties other than the standard ones set by themes. I found several web pages suggesting that one add Thunar-specific styling rules to the `gtk.css` file of one's chosen theme. My efforts to discover exactly what CSS classes or IDs to use were more or less fruitless. Anyway, this looks like the sort of gnarly problem that Linux distributions have to solve: different upstreams (Thunar vs themes) making different assumptions about how things are supposed to work. Good luck! Norman Ramsey