As a theme developer / user, I want to have the `current-cat` / `current-cat-parent` classes on the built-in Categories widget based on the current post

[LongYC]

In order to style the built-in Categories widget according to current post / page,
as a theme developer / user,
I want to have the current-cat / current-cat-parent classes on the built-in Categories widget based on the current post (i.e. on single post / page / custom post type).

Implementing this feature / enhancement will involve modifying wp-includes/category-template.php, specifically Walker_Category#start_el.

This is my first time submitting a ticket here, please correct me if I'm not following any guidelines. I did a search on existing tickets for such feature / enhancement but couldn't find any.

Thank you.

[welcher]

Related #23012