widget button color followup

I see that my previous post was set to resolved so I am posting here.

I placed the Newsletter widget into the sidebar. It displays the name and email fields and submit button.

I still would like to change the color of the button to match other colors on our page.

I read through the Form Style documentation and see the css for changing the color but can not figure out how to implement that change.

When I look under the form code tab it displays both the standard form and widget form code. Neither of these can be edited on that screen and I don’t see the associated CSS displayed anywhere.

Where can I add that CSS to make the color change?

Thanks