public function addCssFile($file, $docRoot = null)
    {
        if (null === $docRoot) {
            $docRoot = $this->getDocRoot();
        }

        $docRoot = (string) $docRoot;

        if ('' !== $docRoot) {
            $docRoot .= DIRECTORY_SEPARATOR;
        }

        $file    = preg_replace('/^https?:\/\/[^\/]+/i', '', $file);
        $abspath = $docRoot . $file;

        $this->getCssFileList()->addFile($file, $abspath);

        return $this;
    }