* { margin: 0; padding: 0; box-sizing: border-box; }
html, body {
  width: 100%; height: 100%;
  overflow: hidden;
  background: #000;
  cursor: none;
  user-select: none;
}
canvas {
  position: fixed;
  top: 0; left: 0;
  pointer-events: none;
}
#bg  { z-index: 1; }
#mid { z-index: 2; }
#fg  { z-index: 3; mix-blend-mode: screen; }