class properties

components.my-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  classNames: ['internal']
});

controllers.application.js

import Ember from 'ember';

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

styles.app.css

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

.internal {
  background-color: aquamarine;
}

.external {
  color: crimson;
}

templates.application.hbs

<h1>Welcome to {{appName}}</h1>

{{my-component class="external"}}

{{outlet}}
<br>
<br>

templates.components.my-component.hbs

I'm renderin'

{{yield}}

twiddle.json

{
  "version": "0.12.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.12.0",
    "ember-template-compiler": "2.12.0",
    "ember-testing": "2.12.0"
  },
  "addons": {
    "ember-data": "2.12.1"
  }
}