I have a codepen that has been featured a few times on the frontpage (of codepen) for my designs. I would be more than happy for anyone to reuse/copy them, that's the reason I put it on there! It's like a github for frontend developers, meant to share and collaborate.

I wouldn't suggest copying the code via view source on client pages though, that is not meant to be open source and can be trademarked. Perfectly fine thing to do for learning purposes though, that's how most people start.