protected function registerStyleSheet()
{
if (($url = $this->getCssUrl()) === '') {
$manager = $this->getApplication()->getAssetManager();
// publish the assets
$url = $manager->publishFilePath(dirname(__FILE__) . DIRECTORY_SEPARATOR . 'assets' . DIRECTORY_SEPARATOR . 'TSlider');
$url .= '/TSlider.css';
}
$this->getPage()->getClientScript()->registerStyleSheetFile($url, $url);
}