#mobile-menu {
    max-height: 0;
    overflow: hidden;
    opacity: 0;
    visibility: hidden;
    transform: translateY(-12px) scale(0.96);
    transition: opacity .25s ease, transform .25s ease, visibility .25s ease;
}

#mobile-menu.open {
    max-height: 520px;
    opacity: 1;
    visibility: visible;
    transform: translateY(0) scale(1);
}