Need CSS drop-down menus added to site

Hi. I have an existing website that has top navigation. I would like to update the navigation throughout the site to CSS drop-down menus. These menus should be search engine friendly. I would like to have the ability to update both the text that shows in the menu, along with URL for each link. The menu should be able to support at least up to 2 sublevels. Some header links won't have any sublevels. These menus should come close to matching the existing look of the menu - screenshot attached. Please ask any questions before bidding.