.back{position: fixed;width: 100%;height: 100%;top: 0px;left: 0px;background: rgba(0,0,0,0.2);z-index: 60;display: none;}
.backNav{position: fixed;top: 160px;left: 0px;width: 100%;height: 100%;z-index: 80;display: none;}
.backImg{width: 1000px;height: 500px;margin: auto;background:url(na_14.jpg) no-repeat center;cursor: pointer;}
.backReduce{display: inline-block;position: absolute;width: 64px;height: 64px;background: url(na_15.png) no-repeat;right: 0px;top: 0px;z-index: 99;cursor: pointer;}
.BackNavSmall{position: fixed;width:250px;height: 250px;top: 60px;left: 10px;cursor: pointer;z-index: 5;display: none;}
.backNavMain{position:relative;z-index:99;width:1000px;margin: auto;}