keep CSS private

components.c-item.js

import Ember from 'ember';

export default Ember.Component.extend({
  classNames: ['item'],
  classNameBindings: ['enabled:enabled:disabled']
});

components.my-component.js

import Ember from 'ember';

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

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  items: [
    {enabled: true},
    {enabled: true},
    {enabled: false},
    {enabled: false}
  ]
});

styles.app.css

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

.item {
  border: 1px solid black;
  margin: 3px;
  width: 200px;
  height: 50px;
}

.enabled {
  background-color: green;
}

.disabled {
  background-color: red;
}

templates.application.hbs

{{#my-component itemsList=items as |item|}}
  {{#component item}}
    hello!
  {{/component}}
{{/my-component}}

templates.components.c-item.hbs

{{yield}}

templates.components.my-component.hbs

{{#each itemsList as |item|}}
  {{yield (component 'c-item' enabled=item.enabled)}}
{{/each}}

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"
  }
}