title: CSS fluid layout: margin-top based on percentage grows when container width increases
body: <p>I'm just learning CSS fluid layouts &amp; responsive design, and I'm trying to use all percentage values with no px values in a layout.</p>
  
  <p>So far it seems to be working, but in one spot, I'm seeing something I didn't expect. I'm trying to put a margin between two vertically stacked divs that changes based on the height of the container. I'd expect that margin to change when I resize the window vertically, but it also grows if you resize it horizontally, which I don't want. What am I missing?</p>
  
  <p>Here's a fiddle. Thanks for your help in advance.</p>
  
  <p><a href="http://jsfiddle.net/gregir/aP5kz/">http://jsfiddle.net/gregir/aP5kz/</a></p>