How to embed a “Pen”
You can access the code directly from BehindTheRabbit (using the tabs “HTML”, “CSS”…) or go to the linked CodePen website. On CodePen you can also change the code as you like and see live what’s the result. When you’re ready, just copy the code and use it in Sandvox.
Most likely, you need to create a Raw HTML object and insert there the “HTML” part of the code. CSS can be added both via Page or Site Code Injection, the usual way.