Extend the body_class function

add_filter(‘body_class’,’top_level_parent_id_body_class’);
function top_level_parent_id_body_class($classes) {
global $wpdb, $post;
if (is_page()) {
if ($post->post_parent) { $ancestors=get_post_ancestors($post->ID); $root=count($ancestors)-1;
$parent = $ancestors[$root];
} else {
$parent = $post->ID; }
$classes[] = ‘top-level-parent-pageid-‘ . $parent; }
return $classes; }


body_class function