This example displays a visually rounded rectangular frame rendered across the full browser window, created with an SVG element that fills the viewport and a `rect` with corner radius set to 40 pixels. The visualization uses D3 v5 within a React framework, employing `d3.select` to append the shape directly to the SVG. The `styles.css` fixes the body dimensions to prevent overflow. The underlying data structure, a hierarchical representation of world countries by region from `countryHeirarchy.json`, is available in the project files but not actively visualized in this minimal layout.