Optimize a Navigation Bar For Desktop and Mobile

Looking to have our navigation menu optimized for mobile and desktop devices. The menu was created in html/css and is 850 px in width. Right now the menu's width is appearing too wide on some desktops, tablets, and mobile devices. We're looking to standardize the width across all platforms. The site is on Go Daddy's Website Builder 6 so there is limited access to the server. We will provide you will all code Go Daddy provides to us.