New Twiddle

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

mouse-enter.component.js

import Ember from 'ember';

export default Ember.Component.extend({
  
  classNames: ['mouse-enter'],
  
  classNameBindings: ['isEntered'],
  
  mouseEnter() {
    this.set('isEntered', true);
  },
  
  mouseLeave() {
    this.set('isEntered', false);
  }
  
});

mouse-enter.template.hbs

{{yield}}

styles.app.css

body {
  margin: 12px 16px;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 12pt;
}

.mouse-enter {
  width: 100px;
  height: 50px;
  border: 1px solid;
}

.is-entered {
  background-color: red;
}

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{mouse-enter}}
<br>
<br>

twiddle.json

{
  "version": "0.10.5",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.8.0",
    "ember-data": "2.8.0",
    "ember-template-compiler": "2.8.0",
    "ember-testing": "2.8.0"
  },
  "addons": {}
}