Looks great! Very clean design, nice and simple. I just have a couple of minor nitpicks:

1. It's billed as keyboard friendly, but there's no obvious keyboard shortcut for opening the list of keyboard commands. I would make a ? shortcut for that, put a hint for it in the page text, and open it as a modal overlay that can be dismissed with Escape.

2. Indent/Outdent. Since there's no other command for [ and ], why require Ctrl? Additionally, you could use , and . (< and >) since they are closer to the home row.

Best of luck with your app, I look forward to seeing how it develops further.