title: Using a directive to add class to host element
body: <p>I am currently learning Angular 2. I understood how to use the Angular <code>Renderer</code> to set an <code>ElementStyle</code>, but now I would like to use the <code>Renderer</code> method: </p>
  
  <pre><code>setElementClass(renderElement: any, className: string, isAdd: boolean) : void
  </code></pre>
  
  <p>My question is how can I import a CSS class to my attribute directive? 
  Do I have to convert my CSS class to JSON?</p>