changing the color of tabs

I am trying to apply custom CSS to just this set of tabs and I can’t get it to change to black. How can I do this? It only gives me a few different options for the style and I need it to be black to match the rest of the page.

Here is the page for reference. https://www.rehabeducation.com/new-template/

It’s not finished yet. I didn’t want to go any further if I can get the gray to change to black.

Thank you in advance