/* ───── Back-to-top button ───── */
#back-to-top {
    position: fixed;
    bottom: 30px;
    right: 30px;
    z-index: 999;
    background: rgba(0,0,0,0.75);
    color: white;
    width: 50px;
    height: 50px;
    line-height: 50px;
    text-align: center;
    font-size: 28px;
    border-radius: 50%;
    text-decoration: none;
    box-shadow: 0 2px 10px rgba(0,0,0,0.3);
    transition: all 0.3s ease;
    display: none;            /* hidden until class .show is added */
}
#back-to-top.show { display: block; }
#back-to-top:hover { background: rgba(0,0,0,0.95); transform: scale(1.1); }