Following one of the lessons, I was introduced to the "Libraries" button in the code editor.
When I push it, I get a list of libraries. That list takes up the space previously used to show the code. But the list is not scrollable. The best I can do is completely drag the code editor up to take the full available height. Even then I'm not able to see to the bottom of the library list.
Chrome: Version 61.0.3163.91 (Official Build) (64-bit)
Mac OSX: El Capitan 10.11.6