diff --git a/README.md b/README.md
index ff35c33..7491e1d 100644
--- a/README.md
+++ b/README.md
@@ -156,7 +156,7 @@ If you also want to remove the `m269-23j`, `nb` and `allowed` commands:
 If you want to remove the M269 styling of notebooks:
 
 1. Open file `~/.jupyter/custom/custom.css` in a text editor.
-2. Delete all lines from the comment marking the start of M269 styling up to the comment ending it.
+2. Delete all lines from the comment marking the start of M269-23J styling up to the comment ending it.
 3. Save the file and close the editor.
 
 ## Licence
diff --git a/custom.css b/custom.css
index 2ba0664..7514bf5 100644
--- a/custom.css
+++ b/custom.css
@@ -1,4 +1,4 @@
-/* Start of M269 notebook styling. */
+/* Start of M269-23J notebook styling. */
 
 /*
 By default, numbered lists use letters and Roman digits in levels 2, 3 and 4.
@@ -11,4 +11,4 @@ Change to decimal digits to match numbering in PDF and HTML book versions.
 /* By default, horizontal lines are very light grey. Change to black. */
 .rendered_html hr {border-top: 1px solid black;}
 
-/* End of M269 notebook styling. */
+/* End of M269-23J notebook styling. */