title: How to align an absolute DIV of unknown height outside a "relative" parent by CSS?
body: <p>Consider a simple <a href="http://jsfiddle.net/mqy4z/" rel="nofollow noreferrer">example</a> with html</p>
  
  <pre><code>&lt;div class="parent"&gt;
      &lt;div class="child"&gt;
      &lt;/div&gt;
  &lt;/div&gt; 
  </code></pre>
  
  <p>and CSS</p>
  
  <pre><code>.parent{
      position:relative;
      background:red;
      width:200px;
      height:40px;
  }
  .child{
      position:absolute;
      top:40px;
      left:30px;
      width:70px;
      height:70px;
      background:blue;
  }
  </code></pre>
  
  <p>to place a DIV with absolute position just beneath its parent (with relative position). 
  <img src="https://i.stack.imgur.com/KsK1l.png" alt="enter image description here">   </p>
  
  <p>In this example, I equaled the absolute's top to the parent relative's height.</p>
  
  <p>How to align the absolute DIV just under the parent when <strong>the height is unknown</strong> (both parent and child)?</p>