html,
body {
  height: 100%;padding:0;margin:0;
}

body {
  background: #000;
  background: radial-gradient(#181818, #000);
  overflow: hidden;
}
body:after {
  background: #181818;
  background: radial-gradient(#000, #555);
  border-radius: 50%;
  bottom: 0;
  content: '';
  left: 0;
  margin: auto;
  position: absolute;
  right: 0;
  top: 0;
  width: 50px;
  height: 50px;
  will-change: transform;
}

canvas {
  display: block;
}