How to add color stripe to top of navigation bar?

Hello,

I'm wondering if it's possible to add a simple orange stripe to the top of the nav bar. I'm not a web design pro but I imagine it might be something like adding a full width div block with a fixed height and making the background color orange. Is it possible to do this somehow? 

I've pasted in a photo of the basic effect I want to achieve. The orange bar is just for style and sits at the top of the nav bar.

The template I'm using is Pacific.

Thanks!

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