html, body {
  margin: 0;
  padding: 0;
  height: 100%;
}

body {
  display: flex;
  justify-content: center; /* horizontal center */
  align-items: center;     /* vertical center */
  flex-direction: column;  /* stack h1 above canvas */
  background-color: #000;  /* optional background */
  color: #fff;             /* optional text color */
  font-family: sans-serif;
  text-align: center;
}