Study Meta Viewport Tag
When does shrink-to-fit happen?
When the page loads, it has already taken up the size of the overflow element and has shrunk the viewport to fit the overflowing content.
The further widening of the content is no longer fitted, as in the shrink-to-fit-demo, neither setTimeout nor changes triggered by the button will result in further layout viewport size fitting.
However, real-world situations are much more complex.