body #myBtn {
      display: none;
      height:40px;
      width:40px;
      position: fixed; /*fixed;*/
      bottom: 40px;
      right: 10px;
      z-index: 99;
      overflow: hidden;
      font-size: 18px;
      border: none;
      outline: none;
      background: url("../images/totop.png") no-repeat 0px 0px;
      color: white;
      cursor: pointer;
      padding: 15px;
      border-radius: 8px;
    }
    
body #myBtn:hover {
    background: url("../images/totophover.png") no-repeat 0px 0px;
    }