RSS feeds may not be mainstream, but they are still popular among tech users. However, many users don’t know how to use RSS feeds, which are usually rendered as raw XML files in browsers. The solution is to include an xml-stylesheet processing instruction within the RSS feed, which provides styling information and transforms the XML feed into a valid HTML document that any browser can render. XSL(T) files provide a way to style the feed, including defining inline CSS styles and importing external CSS files. It’s also possible to use XSLT functions to alter values. Styled XML files are not just limited to RSS feeds; they can also be used for website sitemaps. By using XSL files, users can make their RSS feeds look good and even include information explaining what RSS feeds are.
https://darekkay.com/blog/rss-styling/