A full-screen black rectangle with rounded corners fills the browser viewport, rendered as an SVG element. The visualization demonstrates how to set up a minimal D3.js v5 environment within a React framework, using `d3.select` to target the SVG and dynamically sizing it to the document body’s client height and width. The code appends a single `rect` with a 40-pixel corner radius, showcasing basic SVG attribute manipulation without data or interaction. The stylesheet locks the body’s position to prevent scrolling, ensuring the canvas remains fixed.