Ha, to me it is an improper max width. My biggest peeve with the GitHub web UI is the squished center pane.

I hate that it centers it with giant gutters wasting over half the width of a 4K monitor, should I choose to maximize a browser window. I'd much rather see everything shifted to the left. I'd even be OK with some soft margin still causing regular README text to wrap at a typical width.

But, if there are long code or raw text lines, or any embedded image or markdown table or other structure that is inherently wide, I want it to overflow and use that extra screen space, not get clipped into this ridiculously narrow bowling lane. That's my instinctual desire and the only reason I would expand the browser to full screen, and it is an utter disappointment to try that and be told, "no space for you."

Sorry but do you use full screen windows on a 4K monitor? I doubt any website is really designed to fill anything more than ~1400 horizontal logical pixels.

I don't usually. But if I do, it's because I just encountered something like super-wide content and I want to make use of that big screen. I don't do it because I'd really like to see someone's opinion about how all content should cram into a narrow viewport and have massive blank margins...

The current 13" Macboook Pro has a hardware resolution of 2560x1600. The screen resolution will be the same if you switch off display scaling. Pretty much everyone using one will have maximised windows because it's physically small.

You really need CSS that accounts for resolution and pixel density these days.

I do. In the age of various resolutions and screen sizes and css frameworks, websites can and should be designed to look reasonable on any number of horizontal logical pixels. If it isn't supposed to be wider than 1400px, that's what css's `max-width` is for.