Change only Header Background Color

Hello, I have the Catch Everest Free version. Is it possible to edit JUST the background color of the header? I attempted to change the CSS by pasting the following into the custom CSS: /* Header Background Color */ #masthead { background-color: #000; } /* Content Background Color */ .site { background-color: #000; } But when I changed the #masthead background color; it seemed to change additional color throughout the site. My site is: https://ieo.wp.d.umn.edu/ Any information would be greatly appreciated! Kind regards