Header Code Help

Hello.

I need help to identify the CSS code for the menu (which is transparent) at the top of the site. When scrolling, it changes the opacity but I want to know the code of the original menu, which appears when we are at the top of the site since I want to add opacity to it. I tried navbar-menu and other but didn’t worked. Can anyone help with the code please?

The page I need help with: [log in to see the link]