.back-to-top {
    position: fixed;
    bottom: 15px;
    right: 15px;
    text-decoration: none;
    color: #fff;
    background-color: rgba(0, 0, 0, 0.60);
    font-size: 16px;
    padding: 10px 15px;
    display: none;
}

.back-to-top:hover {
    background-color: rgba(135, 135, 135, 0.50);
}