Add active version class to document body

docs/website/src/theme/Root.js

@@ -1,8 +1,20 @@
 import React, {useState, useEffect} from 'react';
 import {useLocation} from '@docusaurus/router';
+import { useActiveDocContext } from '@docusaurus/plugin-content-docs/client';
 
 // inject overlay content in root element
 export default function Root({children}) {
+  const { activeVersion } = useActiveDocContext();
+
+  useEffect(() => {
+    if (activeVersion) {
+      // Remove all version classes
+      document.body.className = document.body.className.replace(/\bversion-\S+/g, '');
+      // Add the active version class
+      document.body.classList.add(`version-${activeVersion.name}`);
+    }
+  }, [activeVersion]);
+
   return <>{children}<Overlay /></>;
 }