Responsive Nav is a tiny JavaScript plugin which weighs only 1.7 KB minified and Gzip’ed, and helps you to create a toggled navigation for small screens. It uses touch events and CSS3 transitions for the best possible performance. It also contains a “clever” workaround that makes it possible to transition from height: 0 to height: auto, which isn’t normally possible with CSS3 transitions.
CSS Menus Plugins Responsive