private static function get_child_theme_config()
 {
     if (!self::$checkedchildtheme) {
         global $PAGE;
         if (in_array('essential', $PAGE->theme->parents)) {
             $themename = $PAGE->theme->name;
             self::$childtheme = \theme_config::load($themename);
             self::$checkedchildtheme = true;
         }
     }
     return self::$childtheme;
 }