I Broke Gmail

I was replying to an email and I pasted in some text in the reply, and everything in the page went up a little...so I tried doing it again, and I could manage to reproduce it, haha. Check it, it's not easy to spot at a simple glance:

You'll see that the black bar on top is gone, and the reply box is out of it's container and there's a pending thingy at the bottom. You can see that by the lack of scroll bars on the side, I couldn't scroll the page up. Pretty weird :P.

Have a good day :D.