@JoseMarqueses Cool idea! Do you have JQuery loaded as well? You need that library to use its associated $ functions. You can either download the library (I would suggest a minified version) or link directly to a hosted version [e.g. on a Content Delivery Network (CDN)] in your external_scripts list.
If you check the “Settings” of that CodePen, you’ll see that JQuery is listed as a (in fact, the only) dependency:
