Navigation bar white background

I’ve completed a beautiful site with Sydeny pro, now my client has asked if the full width navigation and logo bar can have a white background at all times. I am not a coder and I can’t find how to do this as it’s not the theme design, can anyone please help me with some custom code?

Hello there,

Try adding this CSS code to Appearance > Customize > Additional CSS from dashboard.

    .site-header {
      background-color: #fff !important;

    .btn-menu {
      color: #000;

and set darker menu color from Appearance > Customize > Colors > Header.