A blank, rounded rectangle fills the entire browser viewport with a solid color, creating an empty canvas within an SVG element. The example demonstrates the minimal setup required to render a shape using D3 v5, selecting the SVG with `d3.select` and appending a `rect` element whose dimensions are derived from `document.body.clientWidth` and `clientHeight`. The body is fixed with hidden overflow, ensuring the visualization occupies the full screen without scrollbars. This serves as a foundational template for more complex D3 projects.