Add the follwoing to the <head> of the HTML file.
<script async src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.5/MathJax.js?config=TeX-MML-AM_CHTML"></script>
Create the math with LibreOffice Math, and save it as mml file.
Open mml file by text editor. Paste <math></math> part to the
HTML file.