I think you must have accidentally zoomed in at some point and Safari probably remembers the zoom level when you return to a website. Does pressing Cmd and the Minus sign help?
I am trying to edit and save a route we used last year.
For reasons I do not understand your site, and only your site, has decided to double its size on my monitor. No other website is doing this. Clicking on the screen size, changing monitor resolution, changing monitors, hitting the green button top left, nothing helps.
The real problem is I can't see the bottom of the Save window, so I can't save my changes. Utterly useless. See attached screen shot.
Mac PB Pro, Sierra.
DESKTOP TABLET MOBILE
(no app download required)