title: Center absolute div in another div
body: <p>is there a way to place a absolute div inside his parent centered and above the content with z-index?</p>
  
  <pre><code>&lt;div id="parent"&gt;
      &lt;div id="absolute-centred"&gt;&lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>The size of the parent is unknown. the absolute div should be overlaying the content.</p>