private function loadStyleSheetAsset($css){

        $imageRe = "/url\\s*\\(['|\"]?([^)]*\.(png|jpg|jpeg|gif|svg))['|\"]?\\)/mi";
        $importRe = "/@import\\s*(url\\s*\\()?['\"]?([^;]*)['\"]/mi";
        $fontFaceRe = "/@font-face\\s*\\{(.*)?\\}/mi";
        $fontRe = "/url\\s*\\(['|\"]?([^)'|\"]*)['|\"]?\\)/i";

        //extract images
        preg_match_all($imageRe, $css, $matches);
        if(isset($matches[1])){
            foreach($matches[1] as $match){
                $this->addAsset('img', $match);
            }
        }

        //extract @import
        preg_match_all($importRe, $css, $matches);
        if(isset($matches[2])){
            foreach($matches[2] as $match){
                $this->addAsset('css', $match);
            }
        }

        //extract fonts
        preg_match_all($fontFaceRe, $css, $matches);
        if(isset($matches[1])){
            foreach($matches[1] as $faceMatch){
                preg_match_all($fontRe, $faceMatch, $fontMatches);
                if(isset($fontMatches[1])){
                    foreach($fontMatches[1] as $fontMatch){
                        $this->addAsset('font', $fontMatch);
                    }
                }
            }
        }
    }