body { padding: 15px; }
.page {
    position: relative;
    font-family: 'Helvetica', sans-serif;
    margin-left: 25px;
    margin-right: 25px;
    height: 100%;
    aspect-ratio: 6 / 9;
}
.page-number {
    position: absolute;
    bottom: 0;
    right: 0;
}