Just found this feature, and was interested to try my hand at it.
Chrome - Version 67.0.3396.99 (Official Build) (64-bit)
Mac OS 10.12.6
I can't get into edit anything, it just keeps saying "choose from the right or create a new one" but nothing happens. Apparently trying to copy, or even trying to start a new one puts it in the side eventually as a "new" one, but I can't edit new or existing, the left side of the screen never changes, always has that same message.
I checked and found a bunch of JS errors in the console. I cleared them and clicked around a bit, I caught a screenshot of the one that was most prevalent - see image.
Image of issue: https://imgur.com/a/64wbqm5