.back-to-top {
    position: fixed;
    bottom: 40px;
    left: 40px;
    width: 50px;
    height: 50px;
    line-height: 50px;
    text-align: center;
    font-size: 22px;
    color: #c62828;
    background: #fff;
    border: 2px solid #c62828;
    border-radius: 50%;
    box-shadow: 0 6px 20px rgba(0,0,0,0.15);
    cursor: pointer;
    opacity: 0;
    visibility: hidden;
    transition: all 0.4s ease;
    z-index: 9999;
}
.back-to-top.show {
    opacity: 1;
    visibility: visible;
    transform: translateY(-10px);
}
.back-to-top:hover {
    background: #c62828;
    color: #fff;
    transform: scale(1.1);
}