.back-to-top {
    position: fixed;
    bottom: 30px;
    right: 30px;
    width: 50px;
    height: 50px;
    border-radius: 50%;
    background-color: #333;
    color: white;
    border: none;
    cursor: pointer;
    font-size: 24px;
    display: flex;
    justify-content: center;
    align-items: center;
    opacity: 0;
    transition: opacity 0.3s;
    z-index: 9999;
}

.back-to-top.visible {
    opacity: 1;
}