html, body {
  margin: 0;
  padding: 0;
}
canvas {
  display: block;
}
button {
  position: absolute;
  top: 20px;
  left: 20px;
  padding: 10px 22px;
  font-size: 16px;
  font-family: sans-serif;
  font-weight: 600;
  color: #fff;
  background: #2563eb;
  border: none;
  border-radius: 8px;
  cursor: pointer;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.2);
  transition: background 0.15s, transform 0.1s;
  z-index: 10;
}
button:hover {
  background: #1d4ed8;
}
button:active {
  background: #1e40af;
  transform: scale(0.97);
}