Find the CSS file to update the Upfront Scribe Theme Menu Item Font Colo

Hi, how are you?

I am trying to update the Upfront Scribe Theme Menu Item Font Color I have tried in Appearance -> customize then it loaded Upfront editor then I try to change the color using the hex digit but it does not works.

Currently the top menu item (Home / About / etc) are white color I try to change to different color but not able to find it.

Could you please let me know where can I locate the CSS file so I can update it manually.

Please see attached image high lighted in yellow color

Thank you.

Mike.