Also don't set :show-separators, which is not applied in other sidebars.
See https://gitlab.gnome.org/GNOME/gtk/-/issues/3382
gtk_widget_set_parent (sw, GTK_WIDGET (self));
self->list = GTK_LIST_BOX (gtk_list_box_new ());
- gtk_list_box_set_show_separators (GTK_LIST_BOX (self->list), TRUE);
+ gtk_widget_add_css_class (GTK_WIDGET (self->list), "navigation-sidebar");
gtk_scrolled_window_set_child (GTK_SCROLLED_WINDOW (sw), GTK_WIDGET (self->list));