The visualization displays a blank, rounded rectangle that fills the entire browser viewport, with no data or marks drawn. It uses D3 v5 to select the SVG element and set its width and height based on the document body’s client dimensions, then appends a single `<rect>` with a 40-pixel corner radius. The code logs the viewport size to the console, and the CSS fixes the body to prevent scrolling, leaving the canvas as a pure, empty surface.