title: Codepen dashboard doesn't show content within iframe
body: <p>I've created a pen like <a href="https://codepen.io/mdbootstrap/pen/XzbNdx" rel="nofollow noreferrer">this</a> which contains iframes. Inside a pen everything is correct but when I go to my codepen dashboard, it doesn't show content within an iframe - you can see this <a href="https://codepen.io/mdbootstrap/pens/public/" rel="nofollow noreferrer">here</a> - and I don't know why. Maybe you know what it depends on? Thanks.</p>
  
  <pre><code>&lt;div class="embed-responsive embed-responsive-16by9"&gt;
    &lt;iframe class="embed-responsive-item" src="https://www.youtube.com/embed/mlOiXMvMaZo" allowfullscreen&gt;&lt;/iframe&gt; 
  &lt;/div&gt;
  </code></pre>