title: Bootstrap "jumbotron-narrow" example. how does the style change?
body: <p>I'm going over the bootstrap site example <a href="http://getbootstrap.com/examples/jumbotron-narrow/#" rel="nofollow">http://getbootstrap.com/examples/jumbotron-narrow/#</a>
  and when I hover my mouse over the "About" or "Contact" links a grey rounded box appears around the text. When the mouse leaves the element, the grey rounded box disappears.</p>
  
  <p>This is driving me crazy! I have inspected these elements and gone through the styles applied to them and have gone through every single one of them, all the inherited ones, the whole lot. Can someone go through the css and tell me exactly how this is happening? I expected to find some sort of :hover or :focus css but none exists. Furthermore it is not javascript that is changing the background as I have tested the site with javascript enabled.</p>
  
  <p>Please help and I will love you forever.</p>