#back-to-top {
    position: fixed;
    bottom: 40px;
    right: 40px;
    display: none;
    background: #b61e27;
    color: #fff;
    padding: 10px 15px;
    border-radius: 100%;
    cursor: pointer;
    font-size: 18px;
    z-index: 999;
    transform: rotate(-90deg);
}

#back-to-top:hover {
    background: #81141c;
}