Demo site doesn't render math correctly on Chrome

[agoose77]

Describe the bug

Currently math directives are not rendered properly for me:

This seems to have two causes:

1. Not loading the KaTeX CSS
2. Using output: "mathml" instead of output: "htmlAndMathml"

Reproduce the bug

Visit https://executablebooks.github.io/markdown-it-docutils/ on Google Chrome

List your environment

No response

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