#square {
  background-color: red;
  height: 50px;
  position: absolute;
  width: 50px;
}

#game {
  background-color: #111;
  height: 350px;
  margin: 0 auto;
  overflow: hidden;
  position: relative;
  text-align: center;
  width: 350px;
}

button {
  margin: auto;
  display: block;
}