title: Why do I have to configure z-index to be 9999
body: <p>I'm displaying an image on top of another and need to use : </p>
  
  <pre><code>z-index: 9999
  </code></pre>
  
  <p>I would have though that <code>z-index: 999</code> would be enough as there are not 998 elements overlay-ed over each other. I'm not pasting more code as its not mine and private. </p>
  
  <p>Why would I need to set a z-index so high even when there are just approx 5 images overlay ed over each other currently ?</p>