.go2top {
  background: url("https://images.cnblogs.com/cnblogs_com/xiaoxuetu/522210/o_o_go2top.png") no-repeat scroll left top transparent;
    bottom: 65px;
    color: #444444;
    height: 50px;
    right: 50px;
    position: fixed;
    text-align: center;
    width: 50px;
}
.go2top:hover {
    background-position: -50px top;
}