.back-to-top {
    padding: 10px;
    border-radius: 20px;
    background-color: #3a80c6;
    color: #fff;
    position: fixed;
    left: 50%;
    display: -webkit-box;
    display: -ms-flexbox;
    display: flex;
    -webkit-box-align: center;
        -ms-flex-align: center;
            align-items: center;
    -webkit-box-pack: center;
        -ms-flex-pack: center;
            justify-content: center;
    -webkit-transition: bottom 0.2s;
    transition: bottom 0.2s;
    z-index: 1000;
    cursor: pointer;
  }
  .back-to-top.show {
    bottom: 50px;
    left: 50%;
    -webkit-transform: translate(-50%, -50%);
            transform: translate(-50%, -50%);
  }