We need to manually set up the css node,
since the treeview has children whose css
node is not a direct child of the treeview
css node (header buttons).
tree_view->priv->children = g_list_append (tree_view->priv->children, child);
+ gtk_css_node_insert_after (gtk_widget_get_css_node (GTK_WIDGET (tree_view)),
+ gtk_widget_get_css_node (child_widget),
+ tree_view->priv->header_node);
gtk_widget_set_parent (child_widget, GTK_WIDGET (tree_view));
}