Prevent new menu selection moving to top of page

With the main menu above the header image it was not clear that the page was changing when a new menu choice was made. With some CSS in a child theme for Twenty Sixteen the menu is now below the header image, which is better, however each new menu selection now results in the page settling at the top.
Can anybody help to suggest what could be done to keep the relative positioning of the menu on the screen, between selections, the same, and therefore allow the content to visibly change as the page changes, without scrolling?

Thank you in anticipation.