I think this is supposed to be `extra_css_files` instead.
@@ -136,7 +136,7 @@ html_theme = 'sphinx_rtd_theme'
# 'navigation_depth': 3,
# }
html_context = {
- 'css_files': [
+ 'extra_css_files': [
# CSS that can be used to override theme values.
'_static/theme_overrides.css',
],
