.header{background-color:#f7f7f8;height:42px;line-height:42px;font-size:18px;width:100%;text-align:center;position:relative;border-bottom:1px solid #dedede}.header .back{position:absolute;top:7px;display:block;width:35px;height:30px;text-indent:-100px;overflow:hidden;background:url(../../images/sprite/back.png);background-size:35px 30px}