body {
    margin: 0;
    overflow: hidden;
}

canvas {
    display: block;
}

button {
    background: black;
    opacity: .5;
    border: none;
    color: white;
}

#mainDiv {
    position: absolute;
    z-index: 10;
    left: 10px;
    top: 10px;
    font-family: Arial, Helvetica, sans-serif;
    color: white;
    background: rgba(50,50,50,.5);
}