A blank, rounded-corner rectangle fills the viewport, rendered as an SVG element sized to match the browser window. The visualization uses D3 v5’s `select` and `arc` methods to construct a single `rect` element with no data binding or interactive behavior. The page loads D3 from a CDN, with the SVG styled via CSS to eliminate margins and prevent scrolling. This minimal example demonstrates a static canvas-like backdrop, relying solely on the `attr` method to set width, height, and corner radius of the shape.