This example demonstrates a minimal React application that renders a static text message to the browser. The code defines a simple functional `App` component returning a div with the class "message" and the text "Hello React!", then mounts it into the root DOM element using `ReactDOM.render`. It loads React and ReactDOM from a UMD bundle via unpkg, and styling is applied through a CSS rule in the HTML file. No data sources or interactive behaviors are present; it serves purely as a starter template for integrating React into an Observable-style visualization environment.