Inspectors like Chrome Developer Tools and Firebug are vital to writing custom CSS.
It’s tough to inspect a sub menu that is constantly retracting. Try switching your menu into click mode (UberMenu > Basic Configuration > Trigger). Then your submenus will stay expanded while you investigate them!
One great tool for customizing menu styles is the use of Firebug, a Firefox plugin, or the equivalent Chrome Developer Tools for Google Chrome. These tools allow you to inspect the HTML and the CSS styles, as well as change, add or remove styles temporarily to test changes. It’s by far the best way to fully customize your menu style. You can get Firebug at getfirebug.com. Chrome Developer Tools is built in to Google Chrome and can be accessed by pressing F12.
Here are two a great videos on using Firebug. Just remember: DON’T EDIT THE CORE UBERMENU FILES. Instead, be sure to follow the UberMenu Customization Best Practices.