This book is built by Quarto.

The main branch contains the source code. The gh-pages contains the HTML webpages.

To publish the book to gh-pages, switch to the main branch, and execute the command:

quarto publish gh-pages

The publish command will render the content, copy the output to the gh-pages branch, push that branch to GitHub, and then open a browser to view the site once it is deployed.

More details on publishing a book to GitHub: Link