theme_switcher.services.yml

services:
  theme.negotiator.theme_switcher_negotiator:
    class: Drupal\theme_switcher\Theme\ThemeSwitcherNegotiator
    arguments: ['@router.admin_context', '@entity_type.manager', '@context.handler', '@context.repository']
    tags:
      - { name: theme_negotiator, priority: 12 }