Is there a way to limit CSS selectors by page? For example, "select all divs, but only the divs on page 1"

No, this is complex as divs can span multiple pages, and because it could lead to infinite loops if the style pushes them to page 2 after which the selector no longer matches so the style doesn't apply so they fall back to page 1 and repeat.

You can use a JavaScript two pass process to determine which divs ended up on page 1, and then style them differently by ID or some other selector and then run Prince again.