diff --git a/book/_toc.yml b/book/_toc.yml
index 2de2bae..23fa359 100644
--- a/book/_toc.yml
+++ b/book/_toc.yml
@@ -6,7 +6,7 @@ root: intro.md
 parts:
   - caption: Part with some content # A title for the whole the subtree, e.g. shown above the subtree in ToCs, configuration part of sphinx-external-toc (https://sphinx-external-toc.readthedocs.io/en/latest/intro.html)
     numbered: false                 # Default value (line can be removed), whether to number the chapters/sections in this part, configuration part of sphinx-external-toc (https://sphinx-external-toc.readthedocs.io/en/latest/intro.html)
-    style: numerical                # Default value (line can be removed), sstyle of numbering for this part, configuration part of TeachBooks' version of sphinx-external-toc (https://github.com/TeachBooks/sphinx-external-toc?tab=readme-ov-file#toc-tree-options)
+    style: numerical                # Default value (line can be removed), style of numbering for this part, configuration part of TeachBooks' version of sphinx-external-toc (https://github.com/TeachBooks/sphinx-external-toc?tab=readme-ov-file#toc-tree-options)
     restart_numbering: false        # Default value (line can be removed), whether to restart numbering for this part, configuration part of TeachBooks' version of sphinx-external-toc (https://github.com/TeachBooks/sphinx-external-toc?tab=readme-ov-file#toc-tree-options)
     chapters:
     - file: some_content/overview.md