> for what, a "clean" look? It's to stop the offset shift. Pages with scrollbars and pages without have different document widths but the same viewport width.

> for what, a "clean" look? It's to stop the offset shift. Pages with scrollbars and pages without have different document widths but the same viewport width. When you click between the two, the page "shifts" half a scrollbar width if it's centered. To fix this, Apple made the scrollbar an overlay. That stops the shifting. But then everything on any page with a scrollbar looks off-center. To fix that, Apple made it disappear when it's not being used.