New Twiddle

components.child-component.js

import Ember from 'ember';

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

components.parent-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  tagName: '',
  
  // optional values, can be passed in
  selectorClass: null
});

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;
}

.classFromParent {
  padding: 100px;
}

.classFromController {
  background-color: pink;
}

templates.application.hbs

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

{{parent-component}}

{{parent-component selectorClass="classFromController"}}
<br>
<br>

templates.components.child-component.hbs

Hello world.

templates.components.parent-component.hbs

{{child-component class=(concat 'classFromParent ' selectorClass)}} 

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"
  }
}