title: extend the background of a div to fill the parent div's height
body: <p>I have tried a dozen different solutions and nothing seems to work.</p>
  
  <p><a href="http://betelec.ergonomiq.net/societe/offres-d-emploi" rel="nofollow">http://betelec.ergonomiq.net/societe/offres-d-emploi</a></p>
  
  <p>On the page above, I want the teal background of the left sidenav to extend to the height of the white container around it.</p>
  
  <p>The white container gets its height defined by the height of the largest child div (in this case, the mainbody).</p>
  
  <p>I have tried setting the sidenav's div height to auto, but the div remains fixed height. If I set the div to a very large number like 10000px and have overflow hidden, nothing gets hidden.</p>
  
  <p>I am completely at a loss.</p>