Question

I have a scrolling DIV, which contains a list of many items:

 ___________
|         |^|
| Item1   | |
|_________| |
|         | |
| Item2   | |
|_________| |
|         | |
| Item3   | |
|_________|v|

When the user rolls over a list item, a popup appears describing that item:

 ___________
|         |^|
| Item1   | |
|_________| |
|        _|_|____________________
| Item2 | Description for item 2 |
|________------------------------
|         | |
| Item3   | |
|_________|v|

The dilemma is the scrolling div must have overflow:auto, but the popup wants to be visible outside of the div. So currently, my popup gets chopped off:

 ___________
|         |^|
| Item1   | |
|_________| |
|        _|_|
| Item2 | De|
|________---|
|         | |
| Item3   | |
|_________|v|

HTML

<div id="box">
  <ul>
    <li>
       <h2>Item 1</h2>
       <span>Description for item 1</span>
    </li>
    <li>
       <h2>Item 2</h2>
       <span>Description for item 2</span>
    </li>
    <!-- ... and many other items --->
  </ul>
</div>

CSS

#box {
   width: 10em;
   height: 20em;
   overflow: auto;
}

#box ul {
   line-height: 2em;
}

#box ul li {
   position: relative;
}

#box ul li span {
   display: none;
   position: absolute;
   right: -1em;
   top: 1em;
   height: 1em;
}

#box ul li:hover span {
   display: block;
}

Answer 1

You could try experimenting with position:fixed on the popup element and see if that helps you:

http://jsfiddle.net/SpEb2/