A blank, rounded rectangle fills the entire browser viewport as a standalone SVG canvas. The visualization demonstrates a minimal setup where no data or marks are present, only a styled background shape. The code uses D3 v5 to select the SVG element, set its width and height to the document body’s client dimensions, and append a single `rect` with a 40-pixel corner radius. No axes, scales, or interactions are defined, making this a static, empty canvas.