private function add_css_vars(HTMLElement $element, array &$tpl_vars)
 {
     $tpl_vars['C_CSS_CLASSES'] = $element->has_css_class();
     $tpl_vars['CSS_CLASSES'] = $element->get_css_class();
     $tpl_vars['C_CSS_STYLE'] = $element->has_css_style();
     $tpl_vars['CSS_STYLE'] = $element->get_css_style();
 }