nst geometry = new THREE.PlaneGeometry(size, size);
  const material = new THREE.MeshPhongMaterial({color: 'gray'});
  const mesh = new THREE.Mesh(geometry, material);
  mesh.rotation.x = Math.PI * -0.5;
  scene.add(mesh);
}</pre>
        <p>然后把背景调整为浅蓝(lightblue)</p>

        <pre class="prettyprint showlinemods notranslate lang-js" translate="no">
const scene = new THREE.Scene();
-scene.background = new THREE.Color('white');
+scene.background = new THREE.Color('lightblue');</pre>
      