canvas {
  background: 
    linear-gradient(
      hsl(200, 50%, 80%) 0%, 
      hsl(200, 30%, 95%) 75%)
  ;
  display: block;
}

div {
  height: 100%;
  left: 0;
  position: fixed;
  top: 0;
  width: 100%;
  background: url(https://jackrugile.com/images/misc/skyline-texture.png);
}