title: Assign d3.js Axis a Background Color and Change Layer Ordering
body: <p>Currently when you move the circles around, they will move over the axes and obscure them. I am trying to assign a background color to the axes so the circles move underneath the axe. However using CSS <code>background</code> attribute does not seem to do anything.</p>
  
  <p>How would you create an opaque axis that will be a layer above the circles?</p>
  
  <p>JSFIDDLE: <a href="http://jsfiddle.net/PXw5E/1/" rel="nofollow noreferrer">http://jsfiddle.net/PXw5E/1/</a></p>
  
  <p><img src="https://i.stack.imgur.com/Hg84z.png" alt="enter image description here"></p>