When editing a page using Vector-2022, the font-size for .vector-body becomes 16px instead of the default 14px. This affects everything in .vector-body, including previews, so that the previews show a bigger font-size than what the page gets when you save it.

According to the browser inspector, there is an inline style .vector-body { font-size: 100%; } which overrides the default font-size: calc(1em * 0.875); I haven't been able to figure out exactly where this inline style comes from, but it is only(?) present when you edit a page, not when you view it.