Breaks Firefox's reader mode.

Looks like dog shit on mobile.

I agree that this general style is good, just without some of this page's fuckups.

Chrome's too, but why? It's just plain HTML.

Mobile browsers are assuming you're looking at a legacy page optimized for desktops (widescreen) and have a relatively large virtual screen size by default. They expect you to manually zoom in as necessary. Adding this helps:

  <meta name="viewport" content="width=640, initial-scale=1">
This matches the max-width specified by the CSS. However, a smaller viewport width might be appropriate to increase the text size on mobile.

Safari reader mode on mobile works great. But then again, this is a site where you should not need it.