Revert "widgets: don't set background-color for all widgets"
Revert "widgets: don't set background-color for all widgets"

This breaks too many things to be done at this point.

This reverts commit d93b6f3da922782ed56e36d42743b6c4366d7463.

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