#slider{
    overflow:hidden;
    background-color:#eee;
    /*margin:0 auto;*/
    /*position:relative;*/
    margin-top:20%;
    position:absolute;
}
#slider ul{
    height:150px;
    position:relative;
    list-style:none;
    display:block;
    margin:0;
    padding:0;
}
#slider ul li{
    width:300px;
    height:150px;
    float:left;
    text-align:center;
    line-height:150px;
    position:relative;
}
a.left, a.right{
    position:absolute;
    width:20px;
    height:20px;
    top:40%;
    text-decoration:none;
    background-color:#333;
    color:#fff;
    text-align:center;
    line-height:20px;
}

a.right{
    right:0;
}