#nav {
    opacity: 0;
    transform: translateY(-50px);
    transition: transform 0.75s cubic-bezier(0.25, 1, 0.5, 1), opacity 0.75s cubic-bezier(0.25, 1, 0.5, 1);
}

    #nav.visible {
        opacity: 1;
        transform: translateY(0);
    }