<syle>
    body {
        position: relative;
        min-height: 100vh;
        margin: 0;
        background-color: #eee;
    }
    
    @media (prefers-color-scheme: dark) {
        body {
            background-color: #222;
        }
    }
    
    body::before {
        content: "";
        display: block;
        position: absolute;
        inset: 0;
        background: conic-gradient(
            red,
            orange,
            gold,
            yellow,
            lime,
            aqua,
            dodgerblue,
            blue,
            indigo,
            purple,
            deeppink,
            red
        );
        /* ↓ This makes the checkerboard pattern ↓ */
        mask-image: repeating-conic-gradient(#0000 0% 25%, #000 0% 50%);
        mask-size: 2vmax 2vmax;
    }       
</style>