We can add this code in GtkVersioning: #if GTK_CHECK_VERSION(2, 20, 0) gtk_widget_style_attach(widget); #else widget->style = gtk_style_attach(gtk_widget_get_style(widget), window); #endif It is located at least in the webkit1 and webkit2 widget.
I think we can avoid this now that we no longer have GTK+ 2 support.