html, body {
  margin: 0;
  padding: 0;
  height: 100%;
  overflow: hidden;
  background: white;
  font-family: Arial, sans-serif;
}

#overlay {
  position: relative;
  z-index: 2;
  padding: 20px;
}

canvas {
  display: block;
  height: 100vh;
  width: auto;
  margin: 0 auto;
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 0;
}