#js-pagetop {
  position: fixed;
  width: 40px;
  height: 40px;
  border-radius: 8px;
  background: #999;
  color: #fff;
  bottom: 30px;
  right: 30px;
  cursor: pointer;
  opacity: 0.6;
}
 
#js-pagetop span {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  display: block;
  width: 100%;
  text-align: center;
  font-size: 14px;
}