qdoc: Make table of headers on page be scrollable

Allow a user to scroll the table of headers on a given page independently of the webpage, when the visible space is exceeded.

Use Case

Currently the list of headers is not scrollable, meaning if the list exceeds the visible space, you can not click on any of the items that are at the end of the page.

You can only access those if you scroll the page itself to the end, making them not usable, if you need to scroll to the content first to be able to click on the header in the list.