The clue is when you inspect your nav link element with Chrome inspector on the published site, when it’s white. You can see the color you gave it (blue) in the css for its class, but you can see it’s strikedout, and upper, you can see that another color is given to it, the white, and overiding the blue. And you can see that it’s set on “element style”, meaning it’s not in the css, it’s in the html. Look back at the element declaration in the code and you can see that a color is added.
It always the same logic. I reckon it takes a bit of learning but don’t be afraid of it, what I described happens often and is solved the same way each time.
The forum is made for that Your issue is turned into a solution for others.