private function get_add_element_content($label) {
        global $PAGE, $OUTPUT;

        $bs4 = false;

        $theme = $PAGE->theme;
        if ($theme->name === 'boost') {
            $bs4 = true;
        } else {
            foreach ($theme->parents as $basetheme) {
                if ($basetheme === 'boost') {
                    $bs4 = true;
                }
            }
        }

        if (!$bs4) {
            return $label;
        }
        return $OUTPUT->pix_icon('e/insert', $label);
    }