Problem with Z-Index with Sub-Menu

Site in development: http://fuc.inexo.caI have a menu on the left, that have a
low z-index because the layout have to come on top of this menu.Now, my
problem is that I want to sub-menu to be on top of the layout and the menu.I
try almost everything with z-index but never figure out.The site is on
Joomla 2.5 and the menu is ARI Ext Menu.Any help will be really
appreciated!Thank you so much!Nicolas