I still lose all formatting when copy-pasting code from the pdfs being generated. Why does that need to be a problem? Eg from page 47:

  ---
  title: "An Impressive Book"
  author: "Li Lei and Han Meimei"
  output:
  bookdown::gitbook:
  lib_dir: assets
  split_by: section
  config:
  toolbar:
  position: static
  bookdown::pdf_book:
  keep_tex: yes
  bookdown::html_book:
  css: toc.css
  documentclass: book
  ---

https://bookdown.org/yihui/bookdown/bookdown.pdf