public function css()
 {
     $file = $this->get('file');
     $csspp = new CSSPP($file, CSS_BASE_PATH);
     // Include CSS that was marked for inclusion in the session
     if (array_key_exists('stylesheets', $_SESSION)) {
         foreach (array_unique($_SESSION['stylesheets']) as $stylesheet) {
             $csspp->append("@include '{$stylesheet}';\n");
         }
         unset($_SESSION['stylesheets']);
     }
     header('Content-type: text/css');
     echo $csspp;
 }