:root {
    --background-color: white;
    --text-color: black;
}

@media (prefers-color-scheme: dark) {
    :root {
        --background-color: black;
        --text-color: white;
    }
}

body {
    background-color: var(--background-color);
    color: var(--text-color);
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
}

pre#a {
    display: none;
}

pre#b {
    display: block;
}