Edit in JSFiddle

// adapted from https://medium.com/@necsoft/three-js-101-hello-world-part-1-443207b1ebe1
var scene = new THREE.Scene();
var camera = new THREE.PerspectiveCamera( 75, window.innerWidth/window.innerHeight, 0.1, 1000 );
camera.position.z = 4;

var renderer = new THREE.WebGLRenderer({antialias:true});

renderer.setSize( window.innerWidth, window.innerHeight );

document.body.appendChild( renderer.domElement );

var geometry = new THREE.BoxGeometry( 1, 1, 1 );
var material = new THREE.MeshStandardMaterial( { color: "#433F81" } );
var cube = new THREE.Mesh( geometry, material );
scene.add( cube );

var directionalLight = new THREE.DirectionalLight( 0xffffff, 0.5 );
scene.add( directionalLight );
var light = new THREE.AmbientLight( 0x404040, 5 );
scene.add( light );

var render = function () {
  requestAnimationFrame( render );

  cube.rotation.x += 0.01;
  cube.rotation.y += 0.01;

  renderer.render(scene, camera);
};

render();

html, body {
  margin: 0;
}