Show/Hide
A fixed header is not a good idea for a responsive page since it takes up too much room in the viewport when the page is viewed on a mobile phone.
If the header needs to be in view because it contains an important item like the navigation action tab a better option is to make it show/hide. The header will disappear on scroll down and then reappear on scroll up or when the page bottom is reached.
The item below uses sticky positioning so that it scrolls to the top of the browser/device window and then sticks