Fix storage RTD for newer sphinx

docs/storage/source/conf.py

@@ -105,7 +105,7 @@
 html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
 
 def setup(app):
-   app.add_stylesheet("theme_overrides.css")  # overrides for wide tables in RTD theme
+   app.add_css_file("theme_overrides.css")  # overrides for wide tables in RTD theme
 
 # Theme options are theme-specific and customize the look and feel of a theme
 # further.  For a list of options available for each theme, see the