Nav Menu help!

Hello everyone!

so i recently made a sticky menu bar that stays static when the page is scrolled.

I need help editing the menu bar size though…

It looks like this right now: https://i.imgur.com/lSpJnlf.jpg

I want it to look like this: https://i.imgur.com/TErJ2m3.jpg

what css codes do I need to write to make the blue background bar stretch all the way to the sides of the page?

Please and thank you!