Nav Tab for Nested Categories rather then main categories

I am currently using the modularity lite theme by GPP and the top navigation is broken up into two tabs, the first being a list of categories and the second being a list of pages. If I am to add a nested category, it will still display in the list as a main category. I am looking to create a new drop down tab for each main category. Each tab will then display the nested categories within.

Here is the current coding for the two existing tabs…

<li class=”drop”><span>Blog</span>

<?php wp_list_categories(‘orderby=name&depth=-1&title_li=’); ?>

<li class=”drop”><span>About</span>

<?php wp_list_pages(‘orderby=name&depth=-1&title_li=’); ?>

Any help would be greatly appreciated. Thanks in advance.