I love this take because I had exactly the opposite idea. I thought the combo of remarkably simple text (not even wrapped) with incredible, full width visualizations was chef's kiss. I really like the balance there personally, but I hear you. Does your browser have Reader Mode or something like that? I don't use those tools personally, but I believe they will recast the text parts into something that renders optimally for reading (ideal font size, number of characters per line, etc....).

It may be an artistic/engineering choice to demonstrate what minimizing bloat to an extreme degree looks like.

https://danluu.com/web-bloat/

body { margin: 5%; }

That's all it needs, responsive enough for all devices. He can keep his styleless design but margin is always needed.

Users being able to supply their own stylesheet is a core tenant of CSS. Go nuts and make it look however your heart desires!

reader mode helps.