It's served from a python script using aiohttp, behind nginx, on a $16/year VPS.
I might make a github repo with more details, but in the meantime, here's the server script: https://pastebin.com/ykUeppqc (apologies for pastebin, I don't have access to my github account at present)
Just in case the server dies, there's a video of it here: https://twitter.com/David3141593/status/1388602027484356614