body {
  display: flex;
  flex-direction: column;
  align-items: center;
  background: #222;
  color: #fff;
  font-family: Arial, sans-serif;
}

h1 {
  margin-top: 20px;
}

#pong {
  background: #000;
  display: block;
  margin: 30px auto 0;
  border: 2px solid #fff;
  box-shadow: 0 0 20px #111;
}