public function slideshow_start(lesson $lesson) {
        $attributes = array();
        $attributes['class'] = 'slideshow';
        $attributes['style'] = 'background-color:'.$lesson->properties()->bgcolor.';height:'.
                $lesson->properties()->height.'px;width:'.$lesson->properties()->width.'px;';
        $output = html_writer::start_tag('div', $attributes);
        return $output;
    }