html {
  --side: max(100vw, 100vh);
}

html, body {
  width: 100%;
  height: 100%;
}

body {
  margin: 0;
  overflow: hidden;
  position: fixed;
  background-color: #111;
}

canvas {
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
  width: var(--side);
  height: var(--side);
  position: fixed;
}