New Twiddle

components.my-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  attributeBindings: ['style'],
  expanded: false,
  init() {
    this._super(...arguments);
    this.incrementProperty('count');
  },
  style: Em.computed('expanded', function() {
    if(this.get('expanded')) {
      return `background-color: lightgreen`.htmlSafe();
    } else {
      return `background-color: yellow`.htmlSafe();
    }
  }),
  
  count: 0,

  actions: {
    toggle() {
      this.incrementProperty('count');
      this.toggleProperty('expanded');
    }
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  
});

templates.application.hbs

<h1>Ember Alpha</h1>
{{my-component}}

templates.components.my-component.hbs

<h1>The count is {{count}}</h1>

<button {{action 'toggle'}}>Toggle</button>

{{#if expanded}}
  <ol>
    <li>item</li>
    <li>item</li>
    <li>item</li>
    <li>item</li>
    <li>item</li>
  </ol>
{{/if}}

twiddle.json

{
  "version": "0.10.4",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "alpha",
    "ember-data": "2.7.0",
    "ember-template-compiler": "alpha"
  },
  "addons": {}
}