A blank, rounded rectangle fills the entire browser viewport, rendered in muted gray as a purely visual placeholder. The example demonstrates the simplest possible D3.js v5 SVG setup, drawing a single `<rect>` element that adapts to the window's dimensions. The code logs the viewport's width and height to the console, then uses D3's `select` to append the rectangle with `rx` corner radius to an empty `<svg>`. Styling via CSS fixes the body's position and hides overflow, ensuring the canvas remains static regardless of scroll or resize.