style.css

html, body {
    padding: 0;
    margin: 0;
}

#background {
    background-color: #202020;
    position: fixed;
    top: 0;
    left: 0;
    bottom: 0;
    right: 0;
}

#gameCanvas {
    position: absolute;
    left: 0;
    top: 0;
    right: 0;
    bottom: 0;
    margin: auto;
    display: block;
    image-rendering: -moz-crisp-edges;
    image-rendering: -webkit-crisp-edges;
    image-rendering: pixelated;
    image-rendering: crisp-edges;
}

#gameCanvas:focus {
    outline: 0;
}