The Ponylang Mkdocs Theme was a customized theme based on https://github.com/squidfunk/mkdocs-material for MkDocs of the Ponylang Standard Library documentation.
Over time, it fell further and further behind the squidfunk version. Eventually, this project reached the point where we decided to deprecate it.
The ponyc compiler now contains support for all the features in this customized theme while using the latest squidfunk mkdocs-material theme including the insider's builds.