Could you send me a link to your page, because there is different ways to do this based on your menu. For example, if your hover is using a background image, then you will need to modify the image, or if possible add a background repeat which you could in CSS Menu Wirter.
In general, if you want to make these modifications, reenter the CSS Menu Enter and click the Define Button next to the theme drop down and then click on the Design Tab, and select the Hover tab under background and border and you make the necessary updates there.
