title: overflow:hidden does not clip absolute positioned content
body: <p>I am trying to make a box with scrolling text inside. The problem is, when the text is halfway up the box, it is showing outside it when I expect it to be clipped.</p>
  
  <p>The HTML/CSS is very simple and I have no clue what could be going wrong :</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false">
  <div class="snippet-code">
  <pre class="snippet-code-css lang-css prettyprint-override"><code>#vbox {
    width: 100px;
    height: 500px;
    overflow: hidden;
    background: #afa;
  }
  #vtext {
    position: absolute;
    width: 100px;
    top: 250px;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div id="vbox"&gt;
    &lt;div id="vtext"&gt;
      &lt;p&gt;Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Aenean commodo ligula eget dolor. Aenean massa.&lt;/p&gt;
      &lt;p&gt;Cum sociis natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus.&lt;/p&gt;
      &lt;p&gt;Donec quam felis, ultricies nec, pellentesque eu, pretium quis, sem. Nulla consequat massa quis enim.&lt;/p&gt;
      &lt;p&gt;Donec pede justo, fringilla vel, aliquet nec, vulputate eget, arcu. In enim justo, rhoncus ut, imperdiet a, venenatis vitae, justo.&lt;/p&gt;
      &lt;p&gt;Nullam dictum felis eu pede mollis pretium. Integer tincidunt. Cras dapibus. Vivamus elementum semper nisi.&lt;/p&gt;
      &lt;p&gt;Aenean vulputate eleifend tellus. Aenean leo ligula, porttitor eu, consequat vitae, eleifend ac, enim. Aliquam lorem ante, dapibus in, viverra quis, feugiat a,&lt;/p&gt;
    &lt;/div&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>Isn't "overflow:hidden;" suppposed to hide the overflowing content ?</p>
  
  <p><strong>Edit :</strong></p>
  
  <p>Adding "postion:relative" to the box solves the issue but I'm still puzzled... Could someone explain this behaviour ?</p>