Nav bar for desktop and mobile views

Hey guys

I am just about to start an ecom website project and I’m not sure about the nav bar.

The inspiration i’m looking at has a mega menu in desktop view and a slide out nav for mobile and i don’t know if I should code two seprate nav bars or style the same one in a different way. If any of you have any experience with this I would appreciate your help.

the website im using for inspiration is www.topman.com

thanks again guys