title: Margin left and right only shows on the left
body: <p>I'm trying to put a left and right margin on something that is also 100% width. It seems to put both the left and the right margin on the left size (totaling 200px on the left and not 100px either side. What is the reason for this?</p>
  
  <p>It's demonstrated here:</p>
  
  <p><a href="http://jsbin.com/xomocitono/1" rel="nofollow">http://jsbin.com/xomocitono/1</a></p>
  
  <pre><code>&lt;div id="main"&gt;
    Test
  &lt;/div&gt;
  
  #main {width: 100%; margin-left: 100px; margin-right: 100px; background: red;}
  </code></pre>
  
  <p>Thank you!</p>