/**
* Registers a CSS file.
* @param string $url the CSS file to be registered.
* @param array $options the HTML attributes for the link tag.
* @param string $key the key that identifies the CSS script file. If null, it will use
* $url as the key. If two CSS files are registered with the same key, the latter
* will overwrite the former.
*/
public function registerCssFile($url, $options = [], $key = null)
{
$key = $key ?: $url;
if (is_array($key)) {
$key = current($key);
}
$position = isset($options['position']) ? $options['position'] : self::POS_HEAD;
unset($options['position']);
$this->cssFiles[$position][$key] = $this->renderWrapperTag(Html::cssFile($url, $options), $options);
}
