#back-to-top {
    position: fixed;
    bottom: 20px;
    right: 20px;
    width: 50px;
    height: 50px;
    text-align: center;
    line-height: 50px;
    background: #ff4000;
    color: #ffffff;
    cursor: pointer;
    border-radius: 50%;
    display: none;
    z-index: 1000;
  }