.cd-top {
  display: inline-block;
  height: 50px;
  width: 50px;
  border-radius:4px;
  position: fixed;
  bottom: 30px;
  right: 20px;
  /* image replacement properties */
  overflow: hidden;
  text-indent: 100%;
  white-space: nowrap;
  background: #5066ac url(../images/top-arrow.png) no-repeat center center;
  background-size:40%;
  visibility: hidden;
  opacity: 0;
  -webkit-transition: all 0.3s;
  -moz-transition: all 0.3s;
  transition: all 0.3s;
  box-shadow: 0 5px 10px rgb(83 107 164 / 50%);
}
.cd-top.cd-is-visible {
  /* the button becomes visible */
  visibility: visible;
  opacity: 1;
}
.cd-top.cd-fade-out {
  /* 如果用户继续向下滚动,这个按钮的透明度会变得更低 */
  opacity: 1;
}
.cd-top:hover {
  background-color: #687fc6;
  opacity: 1;
  box-shadow: 0 0 20px rgba(0, 0, 0, 0.15);
}

@media (max-width: 480px){ 
  .cd-top {
    height: 44px;
    width: 44px;
    right: 8px;
    bottom: 8px;
  }
}