On a tangent, if you read the book The 48 laws of Power then you know about all the sidenotes (more like complete side stories) throughout the book. I started reading this book on my smartphone years ago, and it was just an awful reading experience. The real paper book was way more readable, but still very annoying because of the long 'side stories'.
Reminds me of Jonathan Strange and Mr Norrel, tons of footnotes, some of which were their own contained stories. I remember at least one page that was quite literally 3/4ths footnote!
Yes, it did occasionally distract from the novel, but I'm the kind of person that doesn't mind reading and re-reading a passage.
I also liked the content of these side stories, except they made the reading experience harder. Maybe they should have just interspersed them and dedicate a page or two to each side story, now they were spread over the sidelines of multiple pages.
Best migration of foot notes to the web (though the ones that pop up a banner as a sort of ur tool-tip, or expand into a bubble when clicked on are also decent). Most "footnotes" on webpages are actually end-notes, which is mostly a consequence of the lack of distinct pages. Fitting that a blog seemingly about design gets this right.
Edward Tufte's sidenotes. https://edwardtufte.github.io/tufte-css/
"Sidenotes are like footnotes, except they don’t force the reader to jump their eye to the bottom of the page, but instead display off to the side in the margin."
WP style hover footnotes are fine because they are invariably mere bibliographic metadata. (This is also the case for OP, where every sidenote/footnote could, and should, just be a hyperlink.) You know what they are without hovering, because they are just a simple citation and you have zero interest in them unless you are factchecking or following up references. The fact that the footnote is an opaque link, a blackbox, is not an issue when you know what will be inside the blackbox & if it's worth the effort to you - you either want the citation or don't.
However, most of the interesting uses of footnotes people talk about, like nested stories, are not like this. Novels like _House of Leaves_ or _Infinite Jest_ for example. But these are fine also, because you can just assume you want to read the footnote and follow the reference. It just makes reading it more nonlinear and like a CYOA.
However, in between, there is no golden mean. It is very frustrating to have a book where half the footnotes are mere bibliographic information but the other half are interesting comments, digressions, meta-commentary, and so on. You either spend a lot of effort breaking from the text with wasted clicks/context-switches, or you miss a lot of important things. This is bad enough when it's a book using footnotes and you only have to keep glancing down at the bottom to see what it is - but it gets far worse with endnotes, and if they require multiple clicks each, you just give up!
Interesting. I didn't notice the side notes at all because I immediately zoomed my view to only see the main text as I do with all web pages in this day and age.