title: Make div disappear when the page is scrolled to a certain point
body: <p>I have the following block of code, characterising a div:</p>
  
  <pre><code>#posts{
  position:absolute;
  left:150px;
  top:90px;
  width:640px;  
  }
  </code></pre>
  
  <p>And my problem is: when i scroll down, it goes beyond "top:90px". 
  What I'm trying to do is: the part of the div's content which is above <code>top:90px</code> should be invisible. </p>
  
  <p>The thing is... i can't use <code>z-index:(...)</code> because the only thing i have behind this div is the background.</p>