function add($css_file, $media = null, $condition = null, $no_build = false) {
        if(!$css_file) {
            return $this;
        }
        $host = config('larakit.lk-staticfiles.host');
        if(mb_strpos($css_file, '/') === 0 && mb_strpos($css_file, '/', 1) !== 1) {
            $css_file = $host . $css_file;
        }
        $this->css_external[$css_file] = [
            'condition' => $condition,
            'media'     => $media,
            'no_build'  => $no_build,
        ];
        
        return $this;
    }