html, body {
  width: 100%;
  height: 100%;
  margin: 0;
}
canvas {
  width: 100%;
  height: 100%;
  display: block;
}
#menu {
  position: fixed;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  background: rgba(0, 0, 0, 0.85);
  font-family: "Comic Sans MS", sans-serif;
}
#menu[hidden] {
  display: none;
}
#menu .box {
  background: #111;
  border: 2px solid LawnGreen;
  border-radius: 12px;
  padding: 24px 32px;
  text-align: center;
  color: white;
}
#menu h1 {
  color: LawnGreen;
  margin-top: 0;
}
#menu label {
  display: block;
  margin: 12px 0;
  font-size: 1.1em;
}
#menu input {
  width: 4em;
  font-size: 1.1em;
  text-align: center;
  margin-left: 8px;
}
#menu button {
  margin-top: 16px;
  padding: 8px 24px;
  font-size: 1.1em;
  background: LawnGreen;
  border: none;
  border-radius: 6px;
  cursor: pointer;
}