This example creates a full-screen, rounded rectangle that fills the browser viewport. It uses the d3-selection module via `select` to target the SVG element, then dynamically sets the SVG’s width and height attributes based on the document’s client dimensions. A single `<rect>` is appended with a 40-pixel corner radius (`rx`), demonstrating a minimal D3 v5 setup with SVG rendering and no data binding. The styling uses fixed positioning to prevent page scrolling.