Javascript free dropdown (CSS based)

I'm trying to show the basic idea in brief.

instead of using javascript (for example I didn't bother to write crossbrowser supported script)
document.getElementById('div-id').style.visibility ='hidden';
and
document.getElementById('div-id').style.visibility ='visible';

try css as follows where the class for the div would be named as 'menu'
a.menu:link{display: none;}
a.menu:hover{display:block;}

I'll try to explain it in details later.