public function registerCssFile($url, $options = [], $key = null)
{
$url = Yii::getAlias($url);
$key = $key ?: $url;
$depends = ArrayHelper::remove($options, 'depends', []);
if (empty($depends)) {
$this->cssFiles[$key] = Html::cssFile($url, $options);
} else {
$this->getAssetManager()->bundles[$key] = Yii::createObject(['class' => AssetBundle::className(), 'baseUrl' => '', 'css' => [strncmp($url, '//', 2) === 0 ? $url : ltrim($url, '/')], 'cssOptions' => $options, 'depends' => (array) $depends]);
$this->registerAssetBundle($key);
}
}