how to add a css class to control object after the popup menu opened

[romanticyao]

After you click on somthing like User CP in the navbar here, it pops up a menu, How do I modify vbulletin_menu.js so for example when I click on the "User CP" link & after popup opened, it adds a css class to the "User CP" link and after I close the popup, it removes that css class from the link?

Thanx