Floating contents table

Contents table only appears at the very top of the document, and as soon as you scroll down, you lose it.

To access specific parts of a document you either need to scroll all the way back up to the start of the document to consult contents page again, or simply keep scrolling through document until you find what you're looking for. This is very ineffective especially for documents that are very long (like user manuals).

Have a contents table that floats on one side of the document as you scroll through it so you can always refer to it without needing to scroll back up. Having the contents at the top is still useful, the floating contents table would be n addition.