How do i change menu bar color?

Hello, my menu have a nice black background color, but my costumer want to change it, and my theme doesn’t give that option.
I’m trying to debug me site, to find menu css class and make changes, uncessfully, because i am a complete css noob.
I’ve tried:
.nav-container {
color: #656566;
}
but nothing have changed.
My site: https://sandrabastoscoach.com.br/