Improved menu for GtkPopover (3.12)

http://postimg.org/image/7so1osq8z/

http://postimg.org/image/cpf971q1z/

Addition is taken from Adwaita

I only changed in GtkModelButton.button:active:selected:backdrop this: 
color: @theme_unfocused_fg_color;
to
color: @theme_selected_fg_color;