https://www.codecademy.com/courses/learn-jquery/projects/madison-square-market
I don’t understand how the dropdown menu unordered lists are hidden. I don’t see anything in the files making them hidden.
Took me a minute to figure this one out 
dropdown-menu is a predefined class in the bootstrap CSS linked to in the <head>. If you use the developer tools you can see it has a good many values inherited from the bootstrap file, including display: none.