I did look at your design. You said that you would like the nav bar to be visible at all times, and fixed positioning IS a way to achieve this. Of course, you would then have to adjust other things too so that your layout looks the same.
if used fixed positioning, it hides the first Section, which is not we wanted. Even after adjusted the navbar with padding, and when scroll down, it left a padding space, which is not we wanted too. so what else other thing we can adjust?
Anyways i already find the solution by myself by looking the html markup. Body height : auto will solve the problem of the sticky bar that i face instead of body height : 100% .