diff --git a/docs/conf.py b/docs/conf.py
index 7551609cc7e47b59aef8e1565dad47e3089c4c3b..1c11518f557011e8015759f004afbc751d9fdf1b 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -15,7 +15,9 @@ author = 'ccc'
 # -- General configuration ---------------------------------------------------
 # https://www.sphinx-doc.org/en/master/usage/configuration.html#general-configuration
 
-extensions = []
+extensions = [
+    'sphinx_rtd_theme',
+]
 
 templates_path = ['_templates']
 exclude_patterns = ['_build', 'Thumbs.db', '.DS_Store']