Need Help Creating A Stacked Menu Using Nice Menu

I am new to Drupal. I am trying to create a stacked menu in Drupal using nice menu; I want the children menu to be displayed in a stack under the parents like the one displayed on this website http://www.smartvue.com . I tried to modifiy the css code of nice menu changing the position of ul.nice-menu from relative to static:

ul.nice-menu,
ul.nice-menu ul {
z-index: -1;
position: static; (changing it from relative to static, li position as well )

}

#nice-menu-1 li {
position: static;
font-family: Verdana, Geneva, sans-serif;
width: 161 px;
float: left;
text-decoration: none;
font-size: 16px;
list-style: none;
width: 160px;
text-align: center;

}
But it does not seem to work. I will appreciate some styling help.

Thanks!