title: Align left div vertically on middle of right div
body: <p>I made an "arrow" with a div on the left side of another (right) div. Both are inside a container div. I'm trying to align it at the middle of the parent (thus staying aligned at the middle of the right div) with</p>
  
  <pre><code>top: 50%;
  </code></pre>
  
  <p>...But it isn't aligning exactly at the middle. It can be set with "margin-top" but i don't want a fixed value.</p>
  
  <p>Here's the JSFiddle: <a href="http://jsfiddle.net/qhofmgbb/" rel="nofollow">http://jsfiddle.net/qhofmgbb/</a></p>