Keyboard access to menus

Hello,
I’m having a spot of bother getting my drop down menus to be accessible from the keyboard (ie by tabbing) with javascript turned off.

The tab runs through the drop down items, it just doesn’t open the drop down so you can’t actually see whats happening.

I can mouse over it with javascript off & it works okay, and if I hover the mouse over the parent & then tab you can see the different items being highlighted.

Does wordpress have problems opening dropdowns when tabbing through them, or is there a simple css control missing?

I’ve tried adding a:focus & a:active but it isn’t working.

Many Thanks.