list all category posts, but highlighting selected category
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I'm not sure how to search for this and I hope I can explain this well enough.

I'm using a wordpress.org theme that lists posts by displaying the post's featured image with post title over it.

I'm trying to figure out how to do the following:

When I click on a category, I want to display all available posts, but using some kind of css, highlighting only the items within the selected category.
