A blank rectangular canvas fills the entire browser window, rendered as an SVG rectangle with rounded corners. The visualization demonstrates a minimal starting point where no data or marks are present, leaving the empty space as the primary visual element. The code uses D3 v5 to select the SVG element, measure the document’s client width and height, and append a single rectangle with a 40-pixel corner radius. Styling is handled via fixed positioning in CSS to prevent scrolling overlow.