style.css

* {
  box-sizing: border-box;
  margin: 0;
}
body {
  background: #111;
  overflow: hidden;
}
canvas {
  display: block;
  touch-action: none;
}

#loading {
  position: fixed;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  background: #111;
  color: rgba(255, 255, 255, 0.4);
  font: 12px monospace;
  z-index: 100;
  transition: opacity 0.4s;
}
#loading.done {
  opacity: 0;
  pointer-events: none;
}