config/gtk-3.0/gtk.css

   1 /* gvim */ #gtk-tooltips {
   2     color: #fff;
   3     background: #000;
   4 }
   5 
   6 .thunar .sidebar treeview,
   7 .nemo-places-sidebar treeview,
   8 .caja-navigation-window treeview {
   9     font-weight: 600;
  10 }