Two scrollbars on custom help html page.

I'm documenting my projects with the Help browser but my help page gets two scrollbars:

The html file is as simple as having a title (with text) in the header and a p (with text) in the body. All tags are closed in the right order and it seems to work on Firefox. I've already tried using html { overflow: hidden; } on the header but it just removes the scrollbar and crops to whatever is visible on the top of the page. How can I get the text to behave like in the official documentation?