Because it is necessary to click a list item to produce the submenu I said that it was not possible using CSS as you cannot have a click followed by another click (all the second click would do is cancel the first click).
However, after playing around with the idea for some time, I have found a way to use hover on the main menu to produce the submenu which can then be clicked.
This does require that all the sublevel lists are the same height irrespective of the number of submenu items. If they were different heights than the top level items would jump around with no control as each top level was selected.
So this is the most basic of menus to show the principle. No doubt it can be refined and styled further, but for now this is it.
It works in IE6, Firefox 18.104.22.168, Opera 9, can be made to work in IE5.5 with a couple of hacks.
Oh....and it stays in shape no matter what font size is selected.
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