how to add id or css attribute for menu-item?

[gavinju]

Please help me, everybody.
How can I add id or class attribute for menu-item?
I want to do something in javascript or css. But now, there is not id or class attribute in the menu-item widget.
Who can help me?
please

[gavinju]

Sorry, I make a mistake.
The word of my subject should be class, not css attribute.