body {
  background-color: #111; /* ほぼ黒 */
  color: white;
  font-family: sans-serif;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  margin: 0;
}

#container {
  text-align: center;
}

canvas {
  border-bottom: 2px solid #00f260; /* 下線だけ引いてみる */
  display: block;
  margin-top: 20px;
}