#btn {
    width: 60px;
    height: 40px;
    position: fixed;
    display: none;
    right: 0px;
    bottom: 30px;
    background: url(/html/images/top.jpg) no-repeat left top;
}
         
#btn:hover {
    background: url(/html/images/top.jpg) no-repeat 0 -40px;
}
         
.box {
    width: 1190px;
    height: 600px;
    margin: 0 auto;
}