To start with, you could add the styles in red:
<font color='"#FF0000"'>max-width: 62.5rem;
margin: 0 auto;</font>
Then you'll just need to fill in the background color on either side. One way to do that is with this:
... though you'll have to set a bg color on things like .row. So an alternative is to wrap the nav in a full width container and pt the background on that instead.