implemented new fitView logic

packages/react/src/components/ViewportPortal/index.tsx

@@ -6,6 +6,31 @@ import type { ReactFlowState } from '../../types';
 
 const selector = (s: ReactFlowState) => s.domNode?.querySelector('.react-flow__viewport-portal');
 
+/**
+ * The `<ViewportPortal />` component can be used to add components to the same viewport
+ * of the flow where nodes and edges are rendered. This is useful when you want to render
+ * your own components that are adhere to the same coordinate system as the nodes & edges
+ * and are also affected by zooming and panning
+ * @public
+ * @example
+ *
+ * ```jsx
+ *import React from 'react';
+ *import { ViewportPortal } from '@xyflow/react';
+ *
+ *export default function () {
+ *  return (
+ *    <ViewportPortal>
+ *      <div
+ *        style={{ transform: 'translate(100px, 100px)', position: 'absolute' }}
+ *      >
+ *        This div is positioned at [100, 100] on the flow.
+ *      </div>
+ *    </ViewportPortal>
+ *  );
+ *}
+ *```
+ */
 export function ViewportPortal({ children }: { children: ReactNode }) {
   const viewPortalDiv = useStore(selector);