Making the primary nav to show where you are

I want to have a css id for the current page I am on on my theme. (meaning that the navigation option will be highlighted for example). While I know how to do it with css, I don't know how to make the id/class appear when using the public_nav_main function.
How am I supposed to do it?


I found the solution by looking in other themes.
If anyone is getting here by looking for the same question the answer is to use "#primary-nav li.current a" in the css, it makes the necessary code to make it happen.