It appears it was a glitch of some kind. There wasn’t any content in any of the edit menus. I exited the browser and when I came back all was well. I figured out the header image using Background Images.
I’ve use Generate Page Header to create a nice parallex header image for what will be my static front page, but the top header (? the one that comes with the free version) is spoiling the design. Is there some way to remove the top header completely? You can see the page in my sandbox here: