Fix CSS so site is readable on iPhone

Currently, this site is unreadable on an iPhone, because the nav-bar is fixed and covers up all of the content. In order to fix that, I just used media queries to hide the nav-bar on devices narrower than 480px. 

(To make this work, I also had to move some embedded CSS you had in the index.html to the style.css file, where it probably should be anyways.)