The Store Code Body Class module for Magento2 adds the website & store code to the body class.
As the name suggests, this plugin simply adds the store & website code to the body class.
composer require samgranger/module-store-code-body-class php bin/magento setup:upgrade
You might have to clear Magento's cache after installation to see the changes depending on your situation.
This module has been released under the MIT license.