This example creates a full-screen, rounded rectangle that fills the browser window. It uses D3 v5 to select the SVG element and dynamically sets its dimensions based on the viewport’s client width and height. The code appends a single `rect` element with a 40-pixel corner radius, rendering a minimal blank canvas. No data is loaded; the focus is purely on establishing a responsive SVG drawing surface using D3’s `select` and attribute manipulation.