Pages as a Drop-Down Menu?

[Idoit Brilliantly]

Does anyone know if it's possible to style links to a Tumblr's sub-pages as a drop-down list?
At the moment, I am using

<div id="pages">
            <ul>
                
                {block:HasPages}
                    {block:Pages}
                        <li>
                            <a href="{URL}" alt="{Label}" title="{Label}">{Label}</a>
                        </li>
                    {/block:Pages}
                {/block:HasPages}
                
            </ul>
        </div>

to have pages display next to each other in my header. I would like them to be in a drop-down list instead, though, since with more pages, the header is simply becoming too long to be displayed properly. Any advice?