黑色风格淡入淡出效果多级菜单，这是来自国外网站的一个特效菜单，理论上可以实现无限级，请根据自己的需求修改吧，应用jQuery技术，很不错！-Black style multi-level menu fade effect, which is a special effect from the foreign website menu, in theory, can achieve unlimited class, please modify it according to their needs