Pydata sphinx theme updates

[jcapriot]

Summary

Updates the css style sheets for the most recent pydata-sphinx-theme versions

PR Checklist

• Linted my code according to the style guides.
• Added relevant method tags (i.e. GRAV, EM, etc.)
• Marked as ready for review (ff this is was a draft PR), and converted
  to a Pull Request

Reference issue

What does this implement/fix?

Some recent updates to the pydata-sphinx-theme have introduced errors in the documentation build, this updates the style sheet, as well as removes some superfluous left behind files that were interfering with the theme.

[codecov]

Codecov Report

Merging #1213 (6506b69) into main (f3f2cad) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1213   +/-   ##
=======================================
  Coverage   81.99%   81.99%           
=======================================
  Files         159      159           
  Lines       24406    24406           
=======================================
  Hits        20011    20011           
  Misses       4395     4395           

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