Automated prefilled pens in parsed markdown

I thought it might be cool if you could rely more on JavaScript to enhance code samples with CodePen prefill embeds. Especially if you're written your article with regular Markdown:

<div class="testing"></div>

.test { width: 20px; height: 20px; background: blue; }

document.querySelector('.testing').classList.add('test');

Couple of issues though:

• The code block tags have to have a specific class name applied to them
• The markup has to be specific too

Just something people will have to be aware of I guess.

A subheading

Here is some more code:

<div class="testing"></div>

.testing { width: 20px; height: 20px; background: red; }