As a recommendation to the author, it would make sense to show the example/demo area the whole time, not only once I scroll down. It confused me. A lot.
WTF? I don't like reading things on the left side of my monitor, so I make the window wider to try and put the text back in the middle. Except now the demo area gets even wider (why? you don't use it for anything but tiny things?).
As I scroll, the various iframe loads create annoying jank, and to top it off, there's a bug at the end of the post where it moves horizontally for no good reason.
If you're going to do stuff like this, you need to polish it waaay better. This reminds me of the UI animations in the new Firefox. A good idea ruined by implementation, would've been better to leave them out.
Desired Reaction: Oh cool, a demo popped up just when it was needed.
My Reaction: Huh? Ugh, that's annoying. Wow, and I scroll back up and it moves again; I didn't ask for that either.