I'd prefer to name this function as to its purpose (toggleCheatsheetVisiblity maybe) rather than by what it does to achieve it (removing and adding CSS). 

Also, it would be better if this could be the same function called when the mode changes. Ideally the cheat sheet would be hidden automatically when the mode is changed, so that Studio doesn't have to have special knowledge of this particular xmodule. I guess that's a question for the future.