Hacker News Reader

No need for a framework or anything of the sort as far as I see it. Establish your scale in some manner which can be converted to a distance relative to the top of the page and position the elements absolutely to their proportional position. You can use this same scale against the scrollY attribute to know where you are relative to the top (in this case for rendering the depth).

Have a look at transform-when[1]. It might suit your needs. Demo can be seen here[2].

[1] https://github.com/callumacrae/transform-when

[2] https://web.archive.org/web/20171203224250/https://samknows....

You could use intersection observer to check the position of an element. I can't remember if there was a native way of doing it in CSS (for some reason it's stored in memory that it was recently added to CSS)... The closest is scroll snap.