body {
  box-sizing: border-box;
  display: grid;
  place-items: center;
  min-height: 100vh;
  margin: 0;
  padding: 24px 12px;
  background: #acaea2;
}

main { width: min(900px, 100%); }
#stage { aspect-ratio: 3 / 2; }
#stage > * { display: block; width: 100%; height: 100%; }