html, body {
  margin: 0;
  padding: 0;
  background: #fafafa;
  overflow: hidden;
  font-family: sans-serif;
}

/* zona magnética central */
#center-zone {
  position: absolute;
  top: 50%;
  left: 50%;
  width: 480px;
  height: 240px;
  transform: translate(-50%, -50%);
  border: 2px dashed rgba(0,0,0,0.2);
  border-radius: 16px;
  pointer-events: none;
}

canvas {
  position: absolute;
  top: 0;
  left: 0;
}