Search Box Background when Clicked

In this screenshot the blue "Search" navigation button link has just been clicked and it is displaying to the center of your screen the search query menu but it's difficult to see the text because the background of the Search menu is transparent and the text is sitting on-top of other text. If it had a background color it would be visible in a more readable fashion. Is there a way I can change that particular background to black?

Perfect, it worked fine..

thank you very much Rideem3..