CH 2020 Stamp Day Basel BS, postal card used as a maximum card cancelled 6.11.-8.11.2020 4000 Basel

Switzerland 2020 Stamp Day Basel BS,
official postal card of Swiss Post (postal stationery) 
"Tag der Briefmarke 2020 Basel", with printed franking unused, without address,
used on the front as a maximum card with a matching special stamp Basler Taube (SBK W75, Michel 1554),
cancelled "6.11.-8.11.2020 4000 Basel - Tag der Briefmarke", luxury conservation.