Kitchen sink -- generic items

[jarrodmillman]

Start implementing this page in our kitchen sink:
https://pydata-sphinx-theme.readthedocs.io/en/stable/examples/kitchen-sink/generic.html

Here is the rough order of priority:

• Math
  Hugo added support for math in markdown in v0.122.0 https://gohugo.io/content-management/mathematics/
  We should replace our custom implementation #366
  It looks like math is broken on the blog, so it would be good to get this done ASAP (see this example)
• Keys / Menu labels
• Centered text
• Sidebars
• References