> Wikipedia is difficult to read due to the small font and large column width.

Narrow columns make text hard to read due to the eye being unable to see whole sentences at once. It's like the "Dick and Jane" books of old: "See Spot! See Spot Run! Run Spot Run!" Books for adults aren't written like that (as print novels attest) and there's a good reason.

What? That's the exact opposite effect that happens with wide columns. With a wide column, your eyes have to scan all the way left to right. With a narrow column, you don't have to scan as much.

Also the largest "adult" books (non-textbooks) that I have take up about 1/5 of my 43" 4k monitors screen. If you aren't adding a healthy text margin, my eyes have to scan left to right twice as much as with a book. If you want to talk about novels - my screen is 8 times as wide as them, so they are naturally using much narrower columns than most websites.

Books for adults aren't given narrow columns in the sense of a newspaper column, but they're absolutely typeset with attention paid to line length -- it's customary to aim for around 55–75 characters per line. On most displays, Wikipedia's lines are, by conventional typography standards, just too darn long.

Use Ctrl(Cmd) and + sign to zoom.

I'm aware, thanks, I'm a developer. That makes the column width wider as well. What you want is a thin column and a large font size, and you can't expect regular users to zoom in.

Regular users won't have a 4k display, or they would have detected the problem in testing. If you have unusual requirements such as a very high ppi display, you can set a minimum font size in your client browser, just as the web was intended to be used since the beginning.

The original idea of the web as a publishing medium was that visualization could be determined by the needs and preferences of the final user, and thankfully the technology still allows for it.

Interestingly, that does work on new wikipedia (good on them) but not on many other sites I tested and has some weird results in some places (for example, it doesn't change the regular text size on HN but makes the "reply" link larger). It seems this doesn't have the desired effect or support and could break things for general use. And unfortunately, as a web dev, I have to primarily work with default settings on.

But those sites would be broken according to spec, no? And certainly they won't satisfy any accessibility guidelines.

Ah, so the problem is that the designer used rem or a mix of em/rem units. I personally use Pixels in everything that way the entire thing zooms and all relationships are proportional.

My takeaway from your comment and my experience is that CSS is a mess of a technology. Oh well.