The best solution I've seen for making sidenotes responsive is to move them into...

AndrewStephens · on April 7, 2020

Those are both very nicely designed sites.

I ended up doing pretty much the same thing. It doesn't work so well for footnotes that are supposed to be linked to a particular work though.

Here is an example from my site with both footnotes and sidenotes[0]. I style the sidenotes to be distinct from normal paragraphs, which can look great or weird depending on the content.

[0] https://sheep.horse/2017/10/how_you_are_reading_this_page.ht...