menubutton: fix theming for linked/raised GtkMenuButton
menubutton: fix theming for linked/raised GtkMenuButton

Theming by Lapo Calamandrei

rgcjonas/adwaita-semidark,rgcjonas/adwaita-semidark,ChrisCummins/gnome-themes-standard,ChrisCummins/gnome-themes-standard,DoctorJellyface/gnome-themes-standard,rgcjonas/adwaita-semidark,ChrisCummins/gnome-themes-standard,Distrotech/gnome-themes-standard,ChrisCummins/gnome-themes-standard,DoctorJellyface/gnome-themes-standard,Distrotech/gnome-themes-standard,ChrisCummins/gnome-themes-standard,rgcjonas/adwaita-semidark