I want to make my nav bar opacity lower but everything inside it to be full opacity?

Here in this website is an example of what I am talking about Link to website.
When I try to do this and set the opacity to half it makes everything in the nav bar at half opacity, how do I make it so its just the opacity of the navbar background?

Instead of opacity use color with alpha value as a background, like rgba(0, 0, 0, .5)

Thanks a lot I will check this solution now.