--- a/Doc/conf.py
+++ b/Doc/conf.py
@@ -65,9 +65,6 @@
 # Options for HTML output
 # -----------------------
 
-html_theme = 'default'
-html_theme_options = {'collapsiblesidebar': True}
-
 # If not '', a 'Last updated on:' timestamp is inserted at every page bottom,
 # using the given strftime format.
 html_last_updated_fmt = '%b %d, %Y'