thanks for getting back and sorry for not being clearer…
this is a vanilla installation of grav without any changes to it so it is using Quark theme and default.md which comes with two pages titled Home and Typography in the menu.
when i flip between these two pages the header (grav icon, site name and menu) remain in position and the body text of the page changes.
it also seems that if i copy one of these pages and change the body text then everything is ok and the header remains in the exactly same place
my issue is that if i create a new page from scratch the header info (grav icon, site name and menu moves slightly to the right in the browser (and back again when i go to one of the original pages) as if there is some extra css padding on the left of the page.