current-cat-ancestor class

I’m looking for a solution to highlight the current-cat-ancestor item on a wp_list_categories list. As I found in the forum, there is still no class added from WordPress by default (like it is for pages with current-page-ancestor). Is there a solution with adding a function, that adds a current-cat-ancestor class???

I’m not very good in php, but I found this function. For some reasons it doesn’t work for me. Anybody sees why?

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