Displaying `category:X` results

With the default blog themes, requesting /category:X gets a page showing the various pages that match that category. I'm creating a new theme (blog-like, but not really a blog) and I want to do the same thing. Do I just have to create a blog.html.twig and blog_item.html.twig pair? Are these file names hard coded somewhere? Or is there a way I can tell Grav what template to load when /category:X is requested? Thanks!

Basically those param-based filters will filter any page that defines a page collection (like blog.md). So you can use them on any page that has a collection defined in it's frontmatter.