body {
    padding: 0;
    margin: 0;
    overflow: hidden;
}

canvas {
    position: absolute;
    left: 0px;
    top: 0px;
}

#canvas1 {
    z-index: 1;
}

#canvas2 {
    z-index: 2;
}

#canvas3 {
    z-index: 3;
}

button {
    position: absolute;
    top: 20px;
    left: 20px;
    z-index: 4;
}