#game{display:block;width:100%;height:100%;border:0;background:#fff}#stage{aspect-ratio:16/9}#stage:fullscreen #game{width:100vw;height:100vh}
@media(max-width:640px){#stage{aspect-ratio:2/3;height:auto;min-height:0;max-height:none}}

#stage:fullscreen{width:100vw;height:100vh;min-height:0;max-height:none;aspect-ratio:auto}