Multiple Canvas Backgrouds

canvas-backgrounds.css

/* CSS */

.background {
    position: fixed;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    background: #333;
    z-index: -1;
}
.canvas {
    position: absolute;
    z-index: -1;
}
.back {
    top: -100px;
    left: -100px;
}
.mid {
    top: -200px;
    left: -200px;
}
.front {
    top: -400px;
    left: -400px;
}