Make a custom 404 page for Jupyter Book

[melaniewalsh]

Last year, I wanted to create a custom 404 page for my Jupyter Book that would maintain its styling and table of contents. This can be tricky to do with Sphinx, but there's a great Sphinx extension called sphinx-notfound-page that makes it possible.

However, as I posted in this issue, I was having some trouble getting the extension to work with my Jupyter Book. But I finally found a solution this week! Here's an example of the 404 page:

To add a custom 404 page like the one above, I installed the sphinx-notfound-page extension, added it to my _config.yml file as an extra extension, and configured it like so:

sphinx:
  extra_extensions:
    - notfound.extension
  config:
    notfound_context:
        body: "<h1>Whoops! Page Not Found</h1>\n\n<p>Sorry, this page doesn't exist. Many sections of this book have been updated recently.</p><p>Try the <a href='https://melaniewalsh.github.io/Intro-Cultural-Analytics/index.html'>home page 🏠 </a> or <a href='https://melaniewalsh.github.io/Intro-Cultural-Analytics/search.html'>search page 🔎 </a> to find what you're looking for.</p>"
    notfound_urls_prefix: "/Intro-Cultural-Analytics/"

The configuration step that finally made the extension work for me was setting notfound_urls_prefix to the name of my repository.