While you can implement sidenavs using just CSS, you can't implement reveal menus which have become the most common nav for simple sites such as portfolios. Ie

While you can implement sidenavs using just CSS, you can't implement reveal menus which have become the most common nav for simple sites such as portfolios. Ie where you start with your fat logo centered and have it shrink into a fixed/sticky top menu/logo as you need to interrogate the scroll position for that.