#toTop:hover{
  background-position:left top;
}

#toTop{
  background:url(https://images.cnblogs.com/cnblogs_com/marvin/640133/o_o_toTop.png) no-repeat -70px top;
  width:57px;
  height:57px;
  overflow:hidden;
  position:fixed;
  right:450px;
  bottom:17px;
  cursor:pointer;
 }