It’s reasonably clear how to close the panel. But the problem isn’t that the user is trying to close the panel and can’t figure out how. Instead, the user sees no reason to close it because they do not know that there’s anything interesting hiding behind it. Then they get overwhelmed by editing markdown syntax without a preview,
I think this is a potential stumbling block for users who are not familiar with markdown editors, and the first few posts is exactly when the learnability of the user interface matters most.