I played a bit more and found out a few bits: - Changing "Style" in XFCE's appearance switches the theme for both GTK+ 2.x and 3.x, no matter what key "gtk-theme-name" of /etc/gtk-3.0/settings.ini and ~/.config/gtk-3.0/settings.ini say though these files are read according to strace
- The GTK+ 3.0 engine for Clearlooks (libclearlooks.so) seems to be provided by both A) x11-themes/gtk-engines-clearlooks-2.91.5 (gnome overlay) B) x11-themes/gtk-engines-2.91.1 (gnome overlay) at different locations: A) /usr/lib64/gtk-3.0/theming-engines/libclearlooks.so B) /usr/lib64/gtk-3.0/3.0.0/engines/libclearlooks.so GTK seems to looks for (A) only according to strace. - Neither package A nor B provide a file /usr/share/themes/Clearlooks/gtk-3.0/gtk.css which is required to even activate the Clearlooks engine. To active the engine, put the line * { engine: clearlooks; } in. Expect this to look ugly. - By putting [Settings] gtk-theme-name = Clearlooks into /usr/share/themes/Clearlooks/gtk-3.0/settings.ini you can produce endless loops. Nice! >From a workaround perspective the most interesting question to me is: where do I get (default or good looking) CSS files for GTK+ 3.0 Clearlooks. Best, Sebastian