A blank rectangular canvas fills the browser window, rendered as a single large SVG rectangle with rounded corners. The code creates this minimal visualization by selecting the `svg` element and setting its dimensions to match the viewport, then appending a `rect` with `rx` for rounded edges. It uses D3 v5's `select` and `json` imports, though no data is loaded or displayed, resulting in an intentionally empty, interactive-free surface. The styling relies on fixed positioning and hidden overflow to ensure the canvas occupies the entire screen.