I have built a stylesheet and sample project for small screen navigation which is currently housed on my Github account. I built this version after using another mobile dropdown by Astuteo which I relly liked, I found myself making the same modification to his work over and over so I took all my changes and publish my own version.

My version works for small and medium screens and uses the nav tag to hold the nested links as well as to provide the background color.

You can change one color value and the entire color scheme works.