A blank, full-viewport SVG canvas displays a single rounded rectangle with softly curved corners. The visualization demonstrates a minimal D3.js v5 setup, using `select` to bind the SVG element and dynamically sizing it to the browser window's client dimensions. It sets the rectangle's width and height to match the viewport, with a corner radius of 40 pixels. The example serves as a clean starting point for building more complex visualizations, with styling applied through an external stylesheet that fixes the body and hides overflow.