Still Nothing Rendering...

I fixed my unreachable code problem but I still have that other problem of nothing rendering.

I was also getting an "undefined" error on React itself, so I turned the script into an ES6 module and imported React which fixed that problem. But still nothing actually gets rendered.

And on CodePen, I get this error:

Uncaught TypeError: Cannot read property 'className' of undefined

on the line

Button.propTypes.className.isRequired();

Why is that?

Also note that on CodePen, changing it into a module wasn't needed.

Anyway, please help me out here as well. Thanks.