Trying to modify or override the out of the box classes and such for the CSS List Menu is more work than if you were to learn how to use the Hierarchical Viewer. Plus if you learn how to use the Hierarchical Viewer, you'll use it more often and in other areas. Did you check out the documentation? There is also a walk through although its for v7. In the walk through there are some items that you can The principal is still the same although in v8 the ability to specify where your sub items go has been added simply by adding this
<cms:SubLevelPlaceHolder runat="server" ID="plcSub" />
A note on your scripts, if your navigation requires scripts, I'd suggest doing your full testing when logged out of Kentico simply because Kentico loads jQuery and several scripts to make the UI function and sometimes they cause issues.