This allows temporary modifications done through
[method@Gtk.StyleContext.add_class],
[method@Gtk.StyleContext.remove_class],
[method@Gtk.StyleContext.set_state] to be quickly
reverted in one go through [method@Gtk.StyleContext.restore].
The matching call to [method@Gtk.StyleContext.restore]
must be done before GTK returns to the main loop.
Saves the @context state.
This allows temporary modifications done through [method@Gtk.StyleContext.add_class], [method@Gtk.StyleContext.remove_class], [method@Gtk.StyleContext.set_state] to be quickly reverted in one go through [method@Gtk.StyleContext.restore].
The matching call to [method@Gtk.StyleContext.restore] must be done before GTK returns to the main loop.