No launch button?

First of all: thanks for the great theme. I really like it!

One thing I cannot figure out: the launch buttons do not show anymore once I switch the theme to "quantecon_book_theme".

This is what I use in my _config.yml:

sphinx:
  config:
    html_theme: quantecon_book_theme
    html_theme_options:
      repository_url: https://github.com/fredzett/CodingBook
      repository_branch: main
      launch_buttons:
        colab_url: https://colab.research.google.com
      persistent_sidebar: true

Is this a bug in the theme or am I doing something wrong?

Reproduce the missing launch button using the _config.yml settings shown in the issue and inspect how quantecon_book_theme handles the launch_buttons option. Compare the generated book with and without the theme, then trace the theme's configuration or template entry point. Done means determining whether the configuration is unsupported or making the Colab launch button appear.