.fm-overlay {
    display: none; /* Hidden by default */
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.5);
    z-index: 9999;
}

    .fm-overlay.show {
        display: flex; /* Visible when JS adds 'show' class */
        align-items: center;
        justify-content: center;
    }