Showing a 'unread' badge on category boxes

Hi, sorry if this behavior already exists, I couldn’t find how to solve my need.

I have a category with several sub-categories shown as boxes. I would like to add a “unread” badge on those with unread messages.

I’ve looked for a css class on these boxes with unread and/or new messages, but couldn’t find any.

Is there a solution for that ?

What I have:

What I’d like to achieve