#scroll-to-top {
    position: fixed;
    bottom: 20px;
    left: 50%;
    transform: translateX(-50%);
    font-size: 16px;
    color: #fff;
    background-color: #333;
    padding: 10px 20px;
    border-radius: 50px;
    text-decoration: none;
    z-index: 9999;
    display: block;
    user-select: none;
    opacity: 0.85;
}
#scroll-to-top.hidden {
    display: none;
}