body {
    background-color: black;
}

#wrapper {
    position: relative;
}

#main-canvas {
    display: block;
    margin: 0 auto;
    /*background-color: darkgray;*/
    position: absolute;
    z-index: 1;
}   

#overlay-canvas {
    display: block;
    margin: 0 auto;
    position: absolute;
    z-index: 10;
}