*{
    padding: 0;
    margin: 0;
    font-family: "Microsoft YaHei";
}
body{
    padding: 25px;
}
.main{
    width:640px;
    height:270px;
    margin: 0 auto;
    position: relative;
}
.main .lunbo-ul{
    width: 640px;
    height:270px;
    list-style-type: none;
    position: relative;
}
.main .lunbo-ul a,img{
    display: block;
}
img{
    width: 100%;
}
.main .lunbo-ul li{
    width: 640px;
    height:270px;
    position: absolute;

}
.btn{
    width: 100px;
    height:270px;
    position: absolute;
    z-index: 99;
    top:0;
    font-size: 50px;
    color:#FFF;
    text-align: center;
    line-height:270px;
    text-shadow: 1px 1px 2px rgba(0,0,0,.31);
    cursor: pointer;
    background: red;
    opacity: .5;
}
.btn-left{
    left:0;
}
.btn-right{
    right:0;
}