Top bar disappears when scrolling down

[dbitouze]

With PST 0.15.1, the top bar disappears when scrolling down:

[drammock]

This is related to https://github.com/pydata/pydata-sphinx-theme/pull/1454/files#diff-c8b78528cfd92c0b193eee9d4af6b8115fdcce4f665ca20c855fbe5334078865 where <header> tag was removed from the top navbar. cc @gabalafou

[gabalafou]

Hmm. Looking into this now.