People work on all different screen sizes, which means the cookbook-making program has to adjust in order to accommodate them all. If you're working on a laptop or desktop and have your browser open to the full size of the screen, you should see this:
If, however, you're working on a smaller screen (like a tablet) or your browser window is smaller than the full screen size, the chapters/recipes and page layout menus will be hidden behind these icons in order to make space: