I found this document https://web.archive.org/web/20130605043221/https://timeline....
It says “The world’s first website and server go live at CERN” on 1990-12-20
It says “The world’s first website and server go live at CERN” on 1990-12-20
the history page here https://timeline.web.cern.ch/timelines/The-birth-of-the-Worl... doesn't list this date - does list the availability of the browser in xmas day