I created a pen, for example this , which contains frames. Everything is correct inside the pen, but when I go to the codepen toolbar, it does not display the contents inside the iframe - you can see here here - And I don’t know why. Maybe you know what it depends on? Thank.
<div class="embed-responsive embed-responsive-16by9">
<iframe class="embed-responsive-item" src="https://www.youtube.com/embed/mlOiXMvMaZo" allowfullscreen></iframe>
</div>
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