The text-only / ad-free nature probably explains a fair bit of my own ... enthusiastic ... readership of HN (recent comment on which: <https://news.ycombinator.com/item?id=34490839>).

As for CSS tweaks, I've applied some modest changes to the basic style which are linked in my profile:

Dred's HN CSS Madhackery: <https://pastebin.com/gLXiqKyd>

Dred's HN CSS Madhackery -- Dark Mode: <https://pastebin.com/6PF3dCXH>

Both can be applied using a CSS style management extension such as Stylus:

<https://add0n.com/stylus.html>

(For Firefox, Chrome, & Opera.)