I’ve been struggling to find out why my about page (Full Page>Page-3) is overlaping my fixed header, when the page scrolls up and down… (I’m not an expert…)
You might find my navigator structure a bit different, that’s because I wanted full pages, have a look at this topic.
I think you maybe need to give your header a z-index value. You do that under Position->advanced->Z-index. The highest z-indez gets to be on top.
Sometimes it looks a bit weird to have a white bg fixed header on top of a content section also with white bg. Maybe you can play with a bit of opacity on the header bg.