JDK1313 on "[Theme: willingness] Is there a way to change the black menu bar to a different color?"

Is there a way to change the black menu bar to a different color?
I looked through the php files and custom css and I don't know where to put the code. And I'm not sure my code is correct either. Can anyone guide me to changing it to a dark gray? Maybe this 636363 so I don;t have to change the font color too.