I tried to follow [this article](https://colinhemphill.com/blog/markdown-syntax-highlighting-with-the-nextjs-app-router) to add code-highlighting to my .mdx-pages. The post states, that once rehypeHighlight is added as a rehype-plugin in next.config.mjs, the code-snippets should be translated as html as seen in the attached image.

But that isn't true for me. For me a code-block is translated like this:

 html
<pre><code class="language-rs">fn main() {
    println!("hello, World!");
}
</code></pre>

so there are no hljs classes. I consequently couldn't style the code-snippets. Any idea why this is happening? What have I done wrong here?

You can look at my next-config and the code in context here: https://github.com/tim-hilt/website/blob/main/next.config.mjs