How to use the multiple themes in one projects?

https://www.drupal.org/project/switch_page_theme

Switch Page Theme module allows to use different theme than the site default theme on specific pages. Module provides functionality to add multiple rules for different themes on specific set of pages for specific roles. This module also support Multi domain & Multilingual sites.

Configuration page path: /admin/config/system/switch_page_theme.

Clear cache to apply the changes.