Sass Attempt

controllers.application.js

import Ember from 'ember';
import scss from '../styles/app';

export default Ember.Controller.extend({
  init() {
    this._super(...arguments);
    Sass.compile(scss, function(result) {
      Ember.$('head').append(`<style>${result.text}</style>`);
    });
  },
  appName: 'Ember Twiddle'
});

styles.app.js

export default `

h1 {
  color: blue;

	span {
  	color: #00c;
	}
}

`;

templates.application.hbs

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

twiddle.json

{
  "version": "0.11.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.10.0",
    "ember-data": "2.10.0",
    "ember-template-compiler": "2.10.0",
    "ember-testing": "2.10.0",
    "sass.js": "https://cdnjs.cloudflare.com/ajax/libs/sass.js/0.10.3/sass.sync.min.js"
  },
  "addons": {}
}