.center{ display: block; position: fixed; _position: absolute; top: 50%; left: 50%; width: 666px; height:400px; margin-left: -333px; margin-top: -200px; z-index: 10001; box-shadow: 2px 2px 4px #A0A0A0, -2px -2px 4px #A0A0A0; background-color: #fff;}

https://www.cnblogs.com/zhangwenjiajessy/p/6130658.html