Hack, hack, hack.
OK. I used mark up of latex and /latex enclosed in brackets instead of the $ a web search indicated.
I could not make the background be white instead of gray so I changed themes to one where it shows up as white by default.
I guess it works. See: https://morford.info/2018/01/22/math-131-january-24-2/ for instance. And changing themes every couple years is like rearranging a room. It doesn’t improve content much, but feels productive.
This is probably supposed to work better than that.
I am using Wiris to get the code to go between the Latex tags.