body {
  margin: 0;
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background: #1b1626;
}

/* Scales the canvas to the largest 16:9 size that fits the window;
   the canvas keeps its 960 x 540 drawing size. */
#game {
  width: min(100vw, calc(100vh * 16 / 9));
  height: auto;
  aspect-ratio: 16 / 9;
}

/* No display value here: it would override the hidden attribute. */
#error-message {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  margin: 12px;
  padding: 10px 14px;
  background: #5c1a1a;
  color: #ffe3d0;
  font-family: "Trebuchet MS", Verdana, sans-serif;
  border-radius: 8px;
}