Hello!
It was built from Cantera sources with some modifications that are described on download page. It's fully offline and has embedded MathJax-3.2.2 (for Doxygen documentation too) for offline equations rendering. The recent upstream fix for continuity equation was added before build.
The tarball is also available via Gentoo Linux app-doc/cantera-docs-3.2.0 package.
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Sergey Torokhov