A blank, rounded rectangle fills the entire browser window. The visualization is a minimal SVG canvas that demonstrates the use of D3 v5's `select` method to resize an SVG element to the full width and height of the viewport. The code appends a single `rect` element with a 40-pixel corner radius, relying on the document's client dimensions. No data or interaction is present; the example focuses solely on the fundamental setup of an SVG drawing space.