diff --git a/requirements.in b/requirements.in
index 1274f91..cbf1e36 100644
--- a/requirements.in
+++ b/requirements.in
@@ -1,2 +1,2 @@
 sphinx
-sphinx-book-theme
+sphinx-rtd-theme
diff --git a/requirements.txt b/requirements.txt
index 1efef67..0f852a6 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -4,24 +4,16 @@
 #
 #    pip-compile requirements.in
 #
-accessible-pygments==0.0.4
-    # via pydata-sphinx-theme
 alabaster==0.7.13
     # via sphinx
 babel==2.13.1
-    # via
-    #   pydata-sphinx-theme
-    #   sphinx
-beautifulsoup4==4.12.2
-    # via pydata-sphinx-theme
+    # via sphinx
 certifi==2023.7.22
     # via requests
 charset-normalizer==3.3.2
     # via requests
 docutils==0.19
-    # via
-    #   pydata-sphinx-theme
-    #   sphinx
+    # via sphinx
 idna==3.4
     # via requests
 imagesize==1.4.1
@@ -31,33 +23,23 @@ jinja2==3.1.2
 markupsafe==2.1.3
     # via jinja2
 packaging==23.2
-    # via
-    #   pydata-sphinx-theme
-    #   sphinx
-pydata-sphinx-theme==0.14.3
-    # via sphinx-book-theme
+    # via sphinx
 pygments==2.16.1
-    # via
-    #   accessible-pygments
-    #   pydata-sphinx-theme
-    #   sphinx
+    # via sphinx
 requests==2.31.0
     # via sphinx
 snowballstemmer==2.2.0
     # via sphinx
-soupsieve==2.5
-    # via beautifulsoup4
 sphinx==6.2.1
     # via
     #   -r requirements.in
-    #   pydata-sphinx-theme
-    #   sphinx-book-theme
+    #   sphinx-rtd-theme
     #   sphinxcontrib-applehelp
     #   sphinxcontrib-devhelp
     #   sphinxcontrib-htmlhelp
     #   sphinxcontrib-qthelp
     #   sphinxcontrib-serializinghtml
-sphinx-book-theme==1.0.1
+sphinx-rtd-theme==0.5.1
     # via -r requirements.in
 sphinxcontrib-applehelp==1.0.7
     # via sphinx
@@ -71,7 +53,5 @@ sphinxcontrib-qthelp==1.0.6
     # via sphinx
 sphinxcontrib-serializinghtml==1.1.9
     # via sphinx
-typing-extensions==4.8.0
-    # via pydata-sphinx-theme
 urllib3==2.0.7
     # via requests
diff --git a/source/conf.py b/source/conf.py
index 128c6bd..25ea9f9 100644
--- a/source/conf.py
+++ b/source/conf.py
@@ -23,5 +23,5 @@
 # -- Options for HTML output -------------------------------------------------
 # https://www.sphinx-doc.org/en/master/usage/configuration.html#options-for-html-output
 
-html_theme = 'sphinx_book_theme'
+html_theme = 'sphinx_rtd_theme'
 html_static_path = ['_static']