CSS: Dropdown Menu - Horizontal with vertical sublevels

gistfile1.css

#main-nav { list-style-type: none; }
#main-nav ul { list-style-type: none; margin: 0; padding: 0; }
#main-nav a { display: block; width: 100%; height: 100%; text-align: center; line-height: 30px; }

/* Universal Level Code */
#main-nav li { width: 175px; height: 30px; }
#main-nav li ul { position: absolute; display: none; }
#main-nav li:hover > ul { display: block; }

/* Level 1 */
#main-nav > li { display: inline-block; }

/* Level 2 */
#main-nav > li > ul > li { position: relative; }

/* Level 3 */
#main-nav > li > ul > li > ul { position: absolute; top: 10%; left: 175px; }