diff --git a/book/_config.yml b/book/_config.yml
index e3c2dfc..cb1ac1c 100644
--- a/book/_config.yml
+++ b/book/_config.yml
@@ -23,6 +23,7 @@ sphinx:
   - sphinx_named_colors
   - sphinx_iframes
   - sphinx_prime_applets
+  - sphinx_dropdown_toggle
   config:
     html_js_files:
     - https://cdnjs.cloudflare.com/ajax/libs/require.js/2.3.4/require.min.js
diff --git a/book/_toc.yml b/book/_toc.yml
index a97c215..176a0d9 100644
--- a/book/_toc.yml
+++ b/book/_toc.yml
@@ -89,6 +89,7 @@ parts:
       - file: external/sphinx-iframes/README.md
       - external: https://github.com/TeachBooks/Sphinx-Indexed-Definitions/blob/manual/README.md #BUMP
       - file: external/Sphinx-PRIME-applets/README.md
+      - external: https://github.com/TeachBooks/Sphinx-Dropdown-Toggle/blob/main/MANUAL.md
     - file: features/visuals.md
       sections:
       - file: external/Sphinx-Image-Inverter/README.md
diff --git a/requirements.txt b/requirements.txt
index 92658c4..062e84c 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -9,6 +9,7 @@ sphinx-proof == 0.2.1
 sphinx-named-colors == 1.0.1
 sphinx-iframes == 1.0.5
 sphinx-prime-applets == 1.0.2
+sphinx-dropdown-toggle == 1.0.0
 
 git+https://github.com/TeachBooks/Sphinx-Thebe