Background Color of Navigation Bar Only

I am trying to change the background color of the navigation bar only, not the entire background of the header.  Any ideas would be greatly appreciated.

Can you share your website URL and a sketch of which bit you want to have a background colour?

Sorry, I thought I had added that.

https://dianespear.squarespace.com/?password=abc123abc

Here's some code to try:

.header-layout-branding-center-nav-center .header-title-nav-wrapper {
  flex: 0 0 100%;
}
.header-layout-branding-center-nav-center .header-title-nav-wrapper .header-nav {
    margin: 0vw 0 0;
    background-color: red;
    padding: 2vw;
}
.header .header-announcement-bar-wrapper {
    padding-bottom: 0vw;
    padding-left: 0vw;
    padding-right: 0vw;
}

Let me know how that's working for you...change the red to any colour you like.

That did it perfectly.  I can't thank you enough!