public static function config($skin, $colour)
    {
        if (!empty($skin) && !empty($colour)) {
            if (!env('APP_CDN', true)) {
                FrontendAsset::add('vendor/icheck/'.$skin.'/'.$colour.'.css');
            } else {
                $version = FrontendAsset::version(class_basename(__CLASS__));
                FrontendAsset::add('https://cdnjs.cloudflare.com/ajax/libs/iCheck/'.$version.'/skins/'.$skin.'/'.$colour.'.css');
            }
        }
    }