title: CSS border on a <div> acts differently?
body: <p>the title may be a little unclear, so here's a screenshot of what I mean:</p>
  
  <p><img src="https://i.stack.imgur.com/6U7B4.png" alt="alt text"></p>
  
  <p><strong><a href="http://pastebin.com/5xPKxicM" rel="nofollow noreferrer">HTML &amp; CSS Sourcecode</a></strong></p>
  
  <p>All elements use the same CSS class, so shouldn't they all have the same width?
  The bigger the border gets, the bigger the difference becomes. How do I make sure the div and the other elements have the same width?</p>
  
  <p>Thanks in advance!</p>