The blog is built with eleventy https://www.11ty.dev/ and as the previous reply already mentioned, the source code is on GitHub [2].
All posts are single Markdown file each with HTML inserted where I need it. The javascript for the demos is custom and changes from post to post. The basic style comes from Sakura CSS [3] with a bunch of custom stuff on top.
[1] https://www.11ty.dev/
[2] https://github.com/FrostKiwi/treasurechest
[3] https://github.com/oxalorg/sakura