Check out the Master List for a great overview. Then style away. For example, use it to determine the menu's font and size. Color sets the initial color shown, but when the user clicks the menu, the options may appear in black. Use Block to override the width of the menu.
Background sets the color of the menu.
The results will not be visible in all browsers though. You can see these settings on the home page of this site. Using Border to set the outside border of the pop-up broke the menu in Netscape 4.x. He's got it all covered. In Browser button on the Toolbar when the page is open, but I think I overlooked telling you that this button also works without first opening the page.