In some cases, you will need to add a class to the body tag of your Magento stores. To process it, you’ll need to set-up an event observer for the layout_render_before event.

1. Create file events.xml on app/code/Magemonkeys/Addbodyclass/etc/frontend

<?xml version="1.0" ?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
  <event name="layout_render_before">
     <observer instance="MagemonkeysAddbodyclassObserverFrontendLayoutLoadBefore" name="add_bodystorecode_class_observer"/>
  </event>
</config>

2. Create file LoadBefore.php on app/code/Magemonkeys/Addbodyclass/Observer/Frontend/Layout

<?php
namespace MagemonkeysAddbodyclassObserverFrontendLayout;
 
use MagentoFrameworkEventObserver;
use MagentoFrameworkViewPageConfig;
use MagentoStoreModelStoreManagerInterface; 

class LoadBefore implements MagentoFrameworkEventObserverInterface
{
   protected $storeManager;

   public function __construct(
       Config $config,
       StoreManagerInterface $storeManager
   ) {
       $this->config = $config;
       $this->storeManager = $storeManager;
   }
 
   public function execute(Observer $observer)
   {
       $store = $this->storeManager->getStore();
       $storeCode = $store->getCode();
       $websiteCode = $store->getWebsite()->getCode();
       $this->config->addBodyClass($storeCode);
       $this->config->addBodyClass($websiteCode);
   }
}