title: Difference between auto, 0, and no z-index?
body: <p>What is the difference between:</p>
  
  <ol>
  <li><code>z-index: auto</code></li>
  <li><code>z-index: 0</code></li>
  <li>no <code>z-index</code> at all</li>
  </ol>
  
  <p>All the above scenarios are for a <code>div</code> that encloses two <code>div</code>s, <code>div1</code> and <code>div2</code> each having a <code>z-index</code> which is <code>9</code> and <code>10</code> respectively.</p>
  
  <p>The enclosing <code>div</code> is in the stacking context of HTML.</p>