Changing the background color of submenu drop-down

I have a child theme and I am trying to figure out how to target the drop-down sub-menus. I would like to change the background color. For example, when you hover over “Photos” in the navigation menu in my left sidebar, “Vintage New York” comes up in the sub-menu popup/drop-down. Is there a way to target these sub-menu items? Right now I am trying to invert the current colors – – I want the background color to be black and the color of the text to be white. Here is my site: http://blog.stompandcrush.com

I can figure out the CSS but I just don’t know how to target this particular element. Any help would be greatly appreciated.