nav: right CONTENT sidebar highlights 2nd header on top window position

[jorgeorpinel]

Right-side CONTENTS element doesn't highlight the right header, at least with scroll 0 in the example below:

https://dvc.org/doc/install/macos

[jorgeorpinel]

Maybe also related: treeverse/dvc.org#750

[shcheklein]

treeverse/dvc.org#750 is not related. In this case the problem is that three and/or more H2 titles are visible. Some of the even above the middle of the page. In this case the heuristic we use to determine which of the titles to highlight decides to show the second one. I think this just an edge case that can be fixed by applying a very specific detection that page is at it's most top or very very close to that and in that case force the very first H2.

[jorgeorpinel]

Also related/ part of the solution: #37