It is a good improvement for the purpose it is intended. However, in my case, on mobile devices (not mobile app; mobile view of webpage), the two buttons narrow the space for content. I have h5p content in my book chapters and the content of h5p don't look neat now; even, crossword puzzle h5p activity does not autosize, and many grids are not visible. It would be good to make these floating buttons optional to be selected on the admin side; maybe you can add it in the following update.
For a faster solution for me now, is there are way to add couple lines of statement to the css of the theme to fix the issue, and disable the floating next/previous buttons while expanding the width of the page to full size? I have tried to add

#mod_book-chaptersnavigation

to the theme css and it hid the buttons, but didn't expand the width to full width. If you could tell me a quick solution to fix it (before any possibel update you may add later), I would really appreciate.

P.S. Please see the attached mobile view screenshots.

Thank you in advance.
Tumer