@media print {
    body * {
        visibility: hidden !important;
    }
    /* …except the modal and its contents */
    #invoices_preview,
    #invoices_preview * {
        visibility: visible !important;
    }
    /* position it at the top of the page */
    #invoices_preview {
        position: absolute;
        top: 0;
        left: 0;
        width: 100%;
    }
}