html,
body {
  height: 100%;
}
body {
  background: #111;
  display: flex;
  align-items: center;
  justify-content: center;
  margin: 0;
}
canvas {
  padding: 20px;
  display: block;
  max-width: calc(100vw - 40px);
  max-height: fit-content;
}