You can do it at the moment with Safari using CSS.
Or alternatively, create a div behind your auto suggest, drop it down to the bottom right (absolute positioning) and give it a shadowy background. Use z-index to get your auto suggest on top of it.
To clarify from the comments, here is some sample CSS
.auto-suggest {
display: block;
width: 200px;
height: 100px;
position: relative;
}
.shadow { /* child of auto-suggest */
display: block;
width: 200px;
height: 100px;
position: absolute;
bottom: -10px;
right: -10px;
background: url(images/shadow.png) no-repeat;
}
Mike, if you can't have a fixed height, you could use JavaScript to calculate the values. jQuery would be a handy library here, and if you're using auto complete, I have a feeling you'll be leveraging a library anyway.