demo/demo1.html

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>My first three.js app</title>
  <style>
   body { margin: 0; }
   canvas { width: 100%; height: 100% }
  </style>
</head>
<body>

</body>
<script src="https://cdn.bootcss.com/three.js/91/three.js"></script>
<script>
var scene = new THREE.Scene();
var camera = new THREE.PerspectiveCamera( 75, window.innerWidth / window.innerHeight, 0.1, 1000 );
var renderer = new THREE.WebGLRenderer();
renderer.setSize( window.innerWidth/2, window.innerHeight/2,false);
document.body.appendChild( renderer.domElement );
// cube
var geometry = new THREE.BoxGeometry( 1, 1, 1 );
var material = new THREE.MeshBasicMaterial( { color: 0x00ff00 } );
var cube = new THREE.Mesh( geometry, material );
scene.add( cube );

camera.position.z = 5;
var animate = function () {
    requestAnimationFrame( animate );
    cube.rotation.x += 0.1;
    cube.rotation.y += 0.1;
    renderer.render(scene, camera);
};
animate();
</script>
</html>