#backToTop {
    position: fixed;
    bottom: 30px;
    right: 30px;
    background: #333;
    color: #fff;
    padding: 0;
    border-radius: 50%;
    font-size: 40px;
    text-decoration: none;
    z-index: 9999;
    opacity: 0;
    transition: opacity 0.3s, background 0.3s;
    width: 60px;
    text-align: center;
}
#backToTop:hover {
  background: #555;
}
#backToTop.show {
  opacity: 1;
}