CustoMenu is css based. So if you want to turn it to your hand, you'll have to know a little about css.
You can add stuff to the customenu css. You can also add stuff to your temlate css. They both are called on, so they both work. But it is easier to keep everything regarding your menu in the customenu css.
with [your classnames] I mean what is already there in the css, or if you use other class names, use that. In the default css, that would be:
div.customenu_style_default div.customenu_default a:hover {