.game-wrapper {
  position: relative;
  width: 100%;
  max-width: 1280px;     /* never bigger than your game’s design width */
  xaspect-ratio: 16 / 9;  /* keeps 1280x720 aspect on all screens */
  margin: 0 auto;        /* center on larger screens */
  background: #000;      /* letterbox color around the game */
  overflow: hidden;
}

/* The iframe fills the wrapper */
.game-frame {
  xposition: absolute;
  xtop: 0;
  xleft: 0;
  width: 1280;
  height: 720;
  border: 0;
  transform-origin: top left;
  display: block;
}