Just a heads-up... The CSS Working Group wants to add a size property to CSS so that developers can set width and height at same time. To avoid colliding with the size property in @page rules, they are asking UAs to internally rename to page-size at parse-time.

https://github.com/w3c/csswg-drafts/issues/820#issuecomment-540711519

Edited 16 Oct 2019 by dauwhe

Thanks for letting us know!