responsive layout breaks

Hi, I am trying to create a website with a responsive layout using skeleton:
http://www.getskeleton.com

here is my website: it breaks when resized to Tablet size and mobile
http://www.jbiddulph.com/skeleton/

tablet
http://www.jbiddulph.com/skeleton/images/screengrab2.jpg

mobile
http://www.jbiddulph.com/skeleton/images/screengrab.jpg

It is because your menu items are floated in all sizes. You’ll have to add media queries to your custom stylesheet, too, to apply different styles with different viewport sizes. Or maybe Skeleton has a few pre-made classes you have to apply?