Technical Documentation Page

https://technical-documentation-page.freecodecamp.rocks/

In the above link, how did they do it? Touching the sub-heading on the left brings us to its related paragraph.

That’s one of the things you learned, creating internal links

I know that but, how did they bring it to the side, is it CSS or HTML? Or any specific code? It’s really amazing, how they did it.

Html, internal links. It’s introduced in the practice projects