Css Drop down menu, how to keep menu infront of content

I have 开发者_JAVA百科created a Css drop down menu but when i hover over a link i can still see the content beneath.

http://ljessett.hndcomputing.net/lewis/

I have tried editing the z-index but that hasnt work any ideas?

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z-index will work but it only works on positioned elements. So you need to position your dropdown menus either by declaring the position property to be either absolute, fixed or relative. In this case I'd suggest going for relative.

Further reading on z-index: http://www.w3schools.com/css/pr_pos_z-index.asp