@keyframes rainbow {
    0% {
        background-color: #66cccc;
    }
    16.67% {
        background-color: #6666cc;
    }
    33.33% {
        background-color: #cc66cc;
    }
    50% {
        background-color: #cc6666;
    }
    66.67% {
        background-color: #cccc66;
    }
    83.33% {
        background-color: #66cc66;
    }
    100% {
        background-color: #66cccc;
    }
}

html, body {
    width: 100%;
    height: 100%;
}

body {
    display: flex;
    align-items: center;
    justify-content: center;
    flex-direction: column;
    margin: 0;
    padding: 1em;
    box-sizing: border-box;
    background-color: #999;
    animation: rainbow 10s linear infinite;
    color: white;
    font-family: system-ui, sans-serif;
    font-size: 24px;
    text-align: center;
}

a {
    color: inherit;
}

img.qr {
    width: 100%;
    max-width: 512px;
    image-rendering: pixelated;
}

a + img.qr {
    margin-top: 1em;
    max-width: 256px;
}