html, body {
  margin: 0;
  padding: 0;
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
}
canvas {
  display: block;
}

#button-holder {
  padding-top: 50px;
  display: flex;
  flex-wrap: wrap;
  width: 400px;
  margin: center;
  justify-content: center;
}