body {
  margin: 0;
  background: #111;
  display: flex;
  justify-content: center;
  align-items: center;
  flex-direction: column;
  height: 100vh;
}

canvas {
  border: 2px solid white;
  background-color: black;
}

#restartBtn {
  margin-top: 10px;
  padding: 10px 20px;
  font-size: 18px;
  display: none;
}