public static function getCacheDir()
 {
     if (empty(self::$_CFAO_CACHE_DIR)) {
         $cache_dir = WP_CONTENT_DIR . '/cfao-cache/' . $_SERVER['HTTP_HOST'] . '/css/';
         self::$_CFAO_CACHE_DIR = trailingslashit(apply_filters('cfao_style_cache_dir', $cache_dir));
     }
     return self::$_CFAO_CACHE_DIR;
 }