body {
}

    /* only show when body has .demo-site */
#page-container.demo-site::before {
    content: "DEMO ONLY";
    position: fixed;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%) rotate(-30deg);
    font-size: 5rem;
    font-weight: bold;
    color: rgba(0, 0, 0, 0.03);
    pointer-events: none; /* so clicks “pass through” */
    z-index: 9999;
    white-space: nowrap;
}