_output.yml

bookdown::bs4_book:
  css: style.css
  config:
    toc:
      #before: |
      #  <li><a href="./">A Minimal Book Example</a></li>
      #after: |
      #  <li><a href="https://github.com/rstudio/bookdown" target="blank">Published with bookdown</a></li>