A full-screen blank canvas renders as a rounded rectangle filling the browser viewport, with no marks or data. The visualization uses D3 v5’s `select` to target the SVG element and sets its dimensions from the document body’s client width and height, then appends a single `rect` with a 40-pixel corner radius. The fixed-position CSS ensures the canvas remains edge-to-edge regardless of scroll, while the empty SVG plus appended rectangle constitutes the entire graphic.