I suggest creating or modifying your existing classes to utilize the classes auto generated by the CMSListMenu. Nice thing is you can specify a comma separated list of node prefixes. For instnace: first, second, third. Then you have a structure like so:
<ul class="firstCMSListMenuUL">
<li class="firstCMSListMenuLI">
menu option 1
</li>
<li class="firstCMSListMenuLI">
menu option 2 w/nested items
<ul class="secondCMSListMentUL">
<li class="secondCMSListMenuLI">
Nested item under menu option 2
</li>
</ul>
</li>
</ul>
You can easily create styles for it in your css.
Another option is to uncheck the box so it will not render the CSS classes dyamically for you.