What’s fun is what actually happens when you try to do these things. It’s disappointing, you can’t even get anywhere near one trillion pixels.
The limits I found five years ago when working at Fastmail, after a customer using IE found their scrollbar broke when they had around 200,000 emails in a mailbox (plus I just checked a couple of them again now):
• Firefox: a few years ago, ignored declarations that resolved to a value higher than 17,895,697 pixels (a smidgeon under 2³⁰ sixtieth pixels). Now, it clamps at that point instead, but maybe three pixels more or less, not immediately clear quite what’s going on and I can’t be bothered investigating. (All browsers seem to have inconsistencies in how clientHeight/getBoundingClientRect/dev tools/whatever report things, that close to the boundaries of possibility. It’s mildly fascinating.)
• IE: ignores declarations that resolve to a value equal to or higher than 10,737,418.23 pixels (2³⁰ − 1 hundredth pixels).
• WebKit: clamps values somewhere around 2²⁵ (~33,554,432) pixels.
• Chromium: matched WebKit when I tested, now it’s clamping around 22,360,882 pixels, but I’m on a 1.5× display, so the 2²⁵ could be connected with device pixels or such. But I think I was on a 2× display when I did the initial testing!
See also https://news.ycombinator.com/item?id=34299569 where I wrote more about it, with links to relevant source code.