html, body {
    margin: 0;
    padding: 0;
    height: 100%;
    width: 100%;
    overflow: hidden;
    background: url("background.jpg") center/cover no-repeat;
}

#scratch {
    position: fixed;
    top: 0;
    left: 0;
    width: 100vw;
    height: 100vh;
}