chess.css

body {
    margin: 0;
}

#loading {
    position: absolute;
    top: 50vh;
    left: 50vw;
    transform: translate(-50%, -50%);
}
#board {
    margin: auto;
    margin-top: calc(100vh/2 - 400px/2);
    width: 400px;
    height: 400px;
}
#board .highlight {
    background: yellow;
    transition: 100ms background;
}
#credits {
    position: absolute;
    bottom: 0;
}

@media screen and (max-device-width: 500px) {
    #board {
        margin: 0;
        width: 100vw;
        height: auto;
    }
}