Changing colour of navbar/ menu on a new installation of version Version 4.0.2.3

Apologies in advance - but I simply can't get my navbar/ menu colour to change. Some of the posts I've seen are quite old and file locations have changed so I was wondering if anyone could definitively describe how to change the colour of the menu/ nav bar with specific file locations for the version stated. Can do a fresh instal if required - very early days. Many thanks.

For the menu you will be needing to look for #menu in ..catalog/view/stylesheet/stylesheet.scss.