#basic-scrolltop-button {
  display: none;
  position: fixed;
  bottom: 20px;
  right: 30px;
  z-index: 99;
  outline: none;
  background: rgba(0, 0, 0, 0.7);
  color: #fff;
  cursor: pointer;
  border-radius: 50%;
  width: 50px;
  height: 50px;
  line-height: 45px;
  text-align: center;
}