An empty SVG canvas fills the browser viewport with a single rounded rectangle, creating a blank slate for visualization. The example demonstrates a minimal React setup where D3 v5 selects the root SVG element and sets its dimensions to match the window. Using the `d3.select` API, the code appends a `rect` element with a 40-pixel corner radius to the SVG, styling it as a softly rounded full-screen backdrop. The rendering relies solely on SVG primitives, with no data binding or interaction logic present.