/* スタイル */
* {
  margin: 0;
  padding: 0;
  overflow: hidden;
}
body {
  height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background: linear-gradient(-45deg,#110f0e 0%, #110f0e 50%, #303030 50%, #303030);
}
canvas {
  margin: 0 auto;
  display: block;
  border: 1px solid #111;
  border-radius: 3px;
  box-shadow: 1px 1px 2px rgba(255,255,255,.2);
}