I think I see the confusion which I do not have a answer for on stock code.
Yes , it is just a comment in the style editor and does not appear on the front end.
If you look at the other comments like
"Pages of Results"
The background color is white or clear.
as well as all the other comments except for
"page selector for the Post list page"
which is a light blue.
Usually they are all the same color
I am not sure where the comments pull their colors from.
Possibly finish up the custom style maybe you still have some edits left in other areas. .
Maybe you customized common.css or admin.css which should have been uploaded by you during the upgrade.
Last edited by Ruben; 02/25/2022 1:23 PM. Reason: Added comment
