html, body {
    margin: 0;
    padding: 0;
    overflow: hidden;
    height: 100%;
    width: 100%;
    background: black;
}
body {
    background: url('background.png') no-repeat center center fixed;
    background-size: cover;
}
canvas {
    position: absolute;
    top: 0;
    left: 0;
    z-index: 2;
    width: 100%;
    height: 100%;
    pointer-events: none;
}