The DrupalX Bootswatch module adds a custom Drush command to apply Bootswatch.com templates to a DrupalX-compatible theme.
This module is already included and enabled by default in the DrupalX distribution.
To apply a Bootswatch theme run the following command:
ddev . drush x-apply-bootswatch
This Drush command will prompt you for the Bootswatch & Drupal theme to apply the styles selected.
After your local _variables.css and _bootswatch files have been updated, run the following commands to recompile your SASS files and clear Drupal caches.
npm run build && ddev . drush cr
Following these commands you should now see your updated styles within your local Drupal instance.