A blank SVG canvas fills the viewport, with a single rounded rectangle covering its full width and height. The code uses D3's `select` to grab the SVG element, then sets its dimensions based on `document.body.clientWidth` and `clientHeight`. A `rect` is appended with `rx` for rounded corners. The visualization demonstrates a minimal setup with D3 v5, React, and SVG, where the data is simply the viewport geometry itself.