Add style class to gedit window
I like transparency and I must create a special theme and run 'env GTK_THEME=geditSpecialTheme gedit' to have transparency in Gedit because Gedit window has no style class (or Id) that would allow me to differentiate it from other windows.
In gedit_window_init(), you can add
gtk_style_context_add_class (gtk_widget_get_style_context (GTK_WIDGET (window)),
"gedit-window");
like in Nautilus : https://gitlab.gnome.org/GNOME/nautilus/blob/master/src/nautilus-window.c#L2655