title: div being pushed down in flexbox
body: <p>I want to prevent green div (<code>.c</code>) being  pushed down, outside the container. </p>
  
  <p><a href="http://codepen.io/anon/pen/vLpPRM?editors=1100" rel="nofollow">http://codepen.io/anon/pen/vLpPRM?editors=1100</a></p>
  
  <pre><code>&lt;section&gt;
   &lt;div class="a"&gt;aaaaaaaa&lt;/div&gt;
   &lt;div class="b"&gt;bbbbb&lt;/div&gt;
   &lt;div class="c"&gt;ccccccccc&lt;/div&gt;
  &lt;/section&gt;
  
  section
    display: flex
    flex-wrap: wrap
    width: 500px
    height: 200px
    background-color: peru
  
  .a
    width: 400px
    height: 100px
    background-color: gray
  .b
    width: 100px
    height: 200px
    background-color: tan
  
  .c
    background-color: green
    height: 100px
    width: 300px
  </code></pre>