Try fingerprinting the css with the current version.

JulienPalard · JulienPalard · commit c6f7c6a4d7d2 · 2021-05-12T10:00:36.000+02:00
diff --git a/python_docs_theme/theme.conf b/python_docs_theme/theme.conf
@@ -1,6 +1,6 @@
 [theme]
 inherit = default
-stylesheet = pydoctheme.css
+stylesheet = pydoctheme.css?2021.5.dev
 pygments_style = default
 
 [options]
