Hover drop-menu like "all departments" tab on ikea.com
I am looking to create a hover drop-menu much like the "All Departments" tab on the http://www.ikea.com/us/en/ navigation bar. I would like to replicate all aspects, including the arrow that goes from point right to down on hover. Can someone please provide me an example on how to acheive this? Any help would be greatly appreciated. The solution needs to work cross-browser and be as accessible as possible.