Hi,
The default CSS List Menu is a basic menu webpart and has no complex styling abilities. Could try to customize it but you'd have to add all your own CSS classes. Perhaps best if you look into the Hierarchical Viewer.
Somewhat older article, but perhaps have a look at the following:
http://devnet.kentico.com/articles/creating-a-mega-menu-using-hierarchical-transformations
Greets,
David