Pin Table of Contents dropdown to the top of the screen when scrolling

[MichSpieler]

Feature Description

Make it possible to pin the Table of Contents dropdown at the top of the screen when a user scrolls down through a chapter.

Feature Use Case

The option to pin the Table of Contents to the top or left-hand side of the screen will allow readers to navigate to other sections without needing to scroll all the way to the top or bottom of the page. This will be especially useful for long sections that would require substantial scrolling.

It will be additionally useful in providing an outline of the full text alongside the section content. Having a sense of the overall structure of the book while reading can be helpful for some learners as they organize and integrate the content into their own knowledge.

Other Notes

User request (link for internal reference)