Content Query Web Part Customization

In one of our organization's Intranet portal there are several Content Query Web Parts that has customized UI example a rotating banner, Latest News & Updates, etc. I am really confused how the CQWP UI has been customized because I have never customize it so far. I checked settings but no reference of any XSL file but still all CQWP has sophisticated customized UI. Any idea how these customization would have been done?