Native select and custom select hybrid, dynamic timer

This was one of the largest projects I've tackled so far, and my code is perhaps a little messy, but it was a good learning experience. In order to include a custom-styled select menu, but still retain the accessibility features of a native select element (which allow only limited styling), I incorporated both and used Javascript to ensure that they interacted properly. Feedback on my JS would be especially welcome, as I'm still unsure of best practices in some areas.