Theming multiple navigational menus

I have a multiple navigational menu which I added through http://localhost/admin/build/menu/add having multiple (ex. given: 5 created navigational) menu including the built-in primary and the secondary menu links. What I wanted to do, is to theme each of those created menus. like in menu “a”, “b” and “c” should have different theme or style.

can anyone please help, how can I achieved this? show or at least link me to where I should start?

thanks,

khaki