If I am writing a Drupal 9+ installation profile/distribution, how can I customize the theme used during the installer?

Question

I'm writing a Drupal installation profile for Drupal 9+. I notice that in versions of Drupal prior to 9.5, Drupal uses the "Seven" theme during installation. After Drupal 9.5, it uses "Claro".

During the installation process, I'd like to use a sub-theme of either Seven or Claro, but that has a custom logo and color scheme. Is there a way to do this?

Answer 1

Yes! Support for this was implemented way back in the early Drupal 8 releases, as part of #1351352.

In the .info file for the installation profile, add the distribution.install.theme key.

For example:

name: 'My Distribution'
type: profile
core_version_requirement: ^9 || ^10
package: 'My Package'
distribution:
  name: 'My Distribution'
  install:
    theme: claro

You can change the distribution.install.theme setting to any theme that's packaged with the distribution. It will automatically get loaded.