GtkStyleContext will be deprecated in gtk 4.10.
https://docs.gtk.org/gtk4/class.StyleContext.html
This preserves code blocks where additional GtkStyleContext operations
were used, such as gtk_style_context_save/restore.
Uses AdwPreferencesPage and AdwPreferencesGroup for
consistency with the rest of the application. The
combo rows now use AdwActionRow so they can be
included in the AdwPreferencesGroup without
a custom list box.