JSFiddle - React, Tailwind, and code Playground

HTML

<script src="//cdn.rawgit.com/mrdoob/three.js/master/build/three.min.js"></script>
<script src="https://threejs.org/examples/js/controls/OrbitControls.js"></script>

CSS

body {
	  margin: 0;
}

JavaScript

let camera, cameraOrtho, scene, renderer, insetWidth, insetHeight, mesh;

init();
animate();

function init() {

  const aspect = window.innerWidth / window.innerHeight;
  const frustumSize = 2;

  camera = new THREE.PerspectiveCamera( 70, aspect, 0.01, 10 );
  camera.position.z = 1;

  cameraOrtho = new THREE.OrthographicCamera( - 0.5, 0.5 , 0.5, -0.5,  0.01, 10 );
  camera.add( cameraOrtho );

  scene = new THREE.Scene();
  scene.add( camera );

  const geometry = new THREE.BoxGeometry( 0.2, 0.2, 0.2 );
  const material = new THREE.MeshNormalMaterial();

  mesh = new THREE.Mesh( geometry, material );
  scene.add( mesh );

  renderer = new THREE.WebGLRenderer( { antialias: true } );
  renderer.setPixelRatio( window.devicePixelRatio );
  renderer.setSize( window.innerWidth, window.innerHeight );
  document.body.appendChild( renderer.domElement );

  window.addEventListener( 'resize', onWindowResize, false );
  onWindowResize();
  
  const controls = new THREE.OrbitControls( camera, renderer.domElement );

}

function onWindowResize() {

  camera.aspect = window.innerWidth / window.innerHeight;
  camera.updateProjectionMatrix();
  
  renderer.setSize( window.innerWidth, window.innerHeight );
  
  insetWidth = window.innerHeight / 4;
  insetHeight = window.innerHeight / 4;
  
  cameraOrtho.aspect = insetWidth / insetHeight;
  cameraOrtho.updateProjectionMatrix();
  
}

function animate() {

	requestAnimationFrame( animate );
  
  mesh.rotation.x += 0.01;
  mesh.rotation.y += 0.02;
  
  renderer.setClearColor( 0x000000 );
  
  renderer.setViewport( 0, 0, window.innerWidth, window.innerHeight );
  
  renderer.render( scene, camera );
  
  renderer.setClearColor( 0x333333 );
  
  renderer.clearDepth();
  
 	renderer.setScissorTest( true );
  
  renderer.setScissor( 16, window.innerHeight - insetHeight - 16, insetWidth, insetHeight );
  renderer.setViewport( 16, window.innerHeight - insetHeight - 16, insetWidth, insetHeight );

	renderer.render( scene, cameraOrtho...