Testing D3
This example displays a plain-text message, “Hello D3, what is going on?” centered on the page. It uses the D3 `select` API to target the `body` element and chain the `.text()` method to set its content. The page loads D3 v7 from a CDN and relies on a CSS class to style the message with a large font size. The visualization demonstrates a minimal D3 setup within a static HTML file, with no external data source.