A single rounded rectangle fills the entire viewport, rendered in SVG with no data or marks. The visualization uses D3 v5’s `select` to bind the SVG element, then sets its width and height to the browser window’s client dimensions. A `rect` is appended with a 40-pixel corner radius, creating a soft-edged blank canvas. The code relies on `document.body.clientWidth` and `clientHeight` for sizing, with the body fixed and overflow hidden via CSS.