This example shows an empty, full-window SVG canvas with a rounded rectangle filling the entire viewport. The visualization resizes to the browser’s current dimensions, logging the width to the console. It uses D3 v6’s `select` function to target the SVG element and append the rectangle, while CSS `body` styles fix the document to the viewport and hide overflow. The code demonstrates a minimal starting point for a blank canvas, with the rounded corners (`rx` attribute) subtly framing the otherwise empty space.