A blank, full-viewport SVG canvas fills the browser window with a single rounded rectangle. The page starts with an empty 960x500 SVG element, then dynamically resizes it to match the document's client width and height using `document.body.clientWidth` and `clientHeight`. The code imports `select` from d3, sets the SVG’s dimensions, and appends a `rect` with a 40-pixel corner radius. No data or interaction is present, demonstrating a minimal d3 SVG setup.