Archive category list into dropdown menu?

Needing some more help with my company’s website. How do I turn the list of archives on the right-hand sidebar on this page – http://my-table.com/sidedish/ – into a dropdown menu that I can style?

<?php $archs = array(
        'type'            => 'monthly',
        'format'          => 'html',
        'show_post_count' => false,
        'echo'            => 1 ); ?>
        <div class="side-archive-list">
        <h2><center>sidedish archives</center></h2>
        <ul align="left">
            <?php //wp_get_archives( $archs ); ?>
            <?php wp_get_post_type_archives('sidedish',$archs) ?>
        </ul>
    </div>

Thank you!