html, body {
  height: 100%;
  margin: 0;
  background: #000;
  overflow: hidden;
  touch-action: manipulation;
}

#c {
  display: block;
  width: 100vw;
  height: 100vh;
}

.hint {
  position: fixed;
  left: 12px;
  bottom: 12px;
  font: 12px/1.4 system-ui, -apple-system, "Segoe UI", sans-serif;
  color: rgba(255,255,255,0.75);
  background: rgba(0,0,0,0.35);
  padding: 10px 12px;
  border: 1px solid rgba(255,255,255,0.15);
  border-radius: 10px;
  user-select: none;
}