I like it! Is it a “home built” functionality or is there a plugin that offers this functionality?
Easy to do with autoform, bootstrap and jquery.
I believe the New Posts banner is a feature of Discourse, which these forums run on: https://github.com/discourse/discourse
I was thinking of the pane, this one that holds the editor. But I assume that is Discourse too. Yes, it is relatively easy to build, but when possible I prefer not to reinvent the wheel