阴影: --可以同时设定多个阴影、用逗号隔开
http://www.fly63.com/article/detial/4726
div { box-shadow: 10px 10px 5px #888888; }div {box-shadow: 10px 10px 20px 10px rgba(255,255,0,0.5), -10px 10px 10px 10px rgba(255,255,255,0.5) }