Ember: Set class on root div element

application.controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
  
  // This is arrow function in > ES6
  addClass: () => {
    
    // Run next, otherwise the DOM is not ready
    Ember.run.next(this, function() {
      
      // Do it with plain JS for > IE10
      document.querySelector('body > .ember-view').classList.add('vanilla-class')
      
      // Or do it with jQuery
      Ember.$('body > .ember-view').addClass('jquery-class')
      
    })
  }.on('init')
  
});

application.template.hbs

<h1>Demo</h1>
<p>Set a class on the root ember-view div.</p>
<p>See it in action the inspector.</p>
<br>
<br>
{{outlet}}
<br>
<br>

twiddle.json

{
  "version": "0.5.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "release",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/2.2.0/ember-data.js",
    "ember-template-compiler": "release"
  }
}