public static function renderCss($options = []) {
		$result = '';
		$list = [];
		$css = Application::get(array('layout', 'css'));
		if (!empty($css)) {
			asort($css);
			foreach ($css as $k=>$v) {
				$script = $k . (strpos($k, '?') !== false ? '&' : '?') . self::getVersion();
				$list[] = $script;
				$result.= '<link href="' . $script . '" rel="stylesheet" type="text/css" />';
			}
		}
		// list is needed for ajax form reloads
		if (!empty($options['return_list'])) {
			return $list;
		}
		return $result;
	}