Create a small background for drop down menu button

Hey,
I have a theme that uses the popular three lines drop down menu button. Once you click the button a drop down menu appears. The problem I’m having is the button is white and blending in with the slider. I want to create a small black background for the menu so its clear where it is. I attached two links one is a photo of the button I’m referring to and the second is the same button but with the background I want

Button: http://lyttonscott.com/wp-content/uploads/2015/11/Screen-Shot-2015-11-06-at-9.37.53-AM.png

Button With Background: http://lyttonscott.com/wp-content/uploads/2015/11/Screen-Shot-2015-11-08-at-10.44.05-PM.png

ps I’m making this for a client so please respond asap ! Thanks in advance