public void style_attach ()
Warning: style_attach is deprecated since "3.0".
This step is unnecessary with StyleContext.
It is a replacement for
widget->style = gtk_style_attach (widget->style, widget->window);
and should only ever be called in a derived widget’s “realize” implementation which does not chain up to its parent class' “realize” implementation, because one of the parent classes (finally Widget) would attach the style itself.