protected function cssminify($content): string
    {
        $content = preg_replace('!/\*[^*]*\*+([^/][^*]*\*+)*/!', '', $content);
        $content = str_replace(': ', ':', $content);
        $content = str_replace(array("\r\n", "\r", "\n", "\t"), '', $content);
        $content = preg_replace("/ {2,}/", ' ', $content);
        $content = str_replace(array('} '), '}', $content);
        $content = str_replace(array('{ '), '{', $content);
        $content = str_replace(array('; '), ';', $content);
        $content = str_replace(array(', '), ',', $content);
        $content = str_replace(array(' }'), '}', $content);
        $content = str_replace(array(' {'), '{', $content);
        $content = str_replace(array(' ;'), ';', $content);
        $content = str_replace(array(' ,'), ',', $content);
        return $content;
    }