title: How to add scroll bar to popup in openlayers 3
body: <p>I'm trying to add the scroll bar to popup with large size using openlayers-3. Anybody help? :-)</p>
  
  <p>I tried..</p>
  
  <pre><code>.popover-content {
      padding: 9px 14px;
      height: 197px;
  }
  </code></pre>
  
  <p>or</p>
  
  <pre><code>div.popup {
      width: 400px;
      width: 200px;
      overflow-y: scroll;
  }
  </code></pre>
  
  <p>but it was bad....</p>