REFACTOR: Remove position fixed from the header and use sticky instead (PR #10781)

This removes fixed positioning from d-header and the topic timeline.

When this is merged a fair number of themes/components that use the above/below header plugin outlet will need some margin/padding adjustments.



is there a change header could be null ?

why not just return header.offsetHeight; ?

note that topic.hbs is overridden by multiple themes, so the merge of this kind of PR should be followed up very cautiously

  const scrollTop = window.scrollY;

Anything is possible! added a check

Do you have any in mind specifically? (I assume it’s an Enterprise customer?) I couldn’t come up with any.

@awesomerobot looks like we have a conflict? Can you resolve. I would love to get this merged :confetti_ball:

@SamSaffron ooh yep, I missed the version bump last week. Will merge once tests pass.