Update swe-book.css
Update swe-book.css

Updates the O'Reilly epub.css to better work on abseil.io. 

Also improves usability for reading large blocks of text by setting a maximum line length per: https://baymard.com/blog/line-length-readability
abseil/abseil.github.io,manshreck/abseil.github.io,abseil/abseil.github.io,abseil/abseil.github.io,manshreck/abseil.github.io,manshreck/abseil.github.io