Title: The table of contents block loses visibility when scrolling the page
As a user, I would like to scroll the content of the page in the book without losing sight of the summary, so I could switch between pages and identify where I am quickly.
Scenario A: When scrolling the page content in a book activity, the table of contents should remain visible until the end of the page.
Scenario B: When I access a book activity with many chapters whose table of contents extends beyond the screen, I should be able to view all chapters without moving the content of the active page.
Scenario C: When I access a book activity with many chapters whose table of contents extends beyond the screen, there should be an indication that there are more chapters.
Scenario D: When scrolling the page content in a book activity and there are other blocks below the TOC, all blocks must be visible when scrolling the page, if there is vertical space for that. If the set of blocks (TOC + others) extend beyond the screen, normal scrolling without sticky.
Use the CSS sticky element in conjunction with the overflow element for the Book's TOC block. Additionally, to indicate the existence of extra chapters that go beyond the screen area, add a shadow scroll. (working in code solution...)