body{
  margin: 0px;
  height:100%;
  width:100%;
  /*background-image:url(image.jpg);/*your background image*/
  background-repeat:no-repeat;/*we want to have one single image not a repeated one*/
  background-size:cover;/*this sets the image to fullscreen covering the whole screen*/
}

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