html, body {
    padding: 0; margin: 0;
    width: 100%; height:100%;
    background: #bababa;
    overflow: hidden;
}

canvas {
    display: block;
    position: fixed;
    top: 0;left: 50%;
    transform: translateX(-50%);
    max-width: 100%;
    max-height: 100%;
    
}

#downloadimage {
    display: none;
    position: fixed;
    top: 0;left: 0;
}