A blank white canvas fills the entire browser viewport, rendered as a single rounded rectangle with no data or interaction. The example demonstrates the minimal setup for a D3.js v5 project using the `select` and `attr` APIs to size and style an SVG element. The code imports utilities from the `d3` module, sets the SVG dimensions to match the window’s `clientWidth` and `clientHeight`, and appends a rectangle with a 40-pixel corner radius. The page uses fixed positioning in CSS to eliminate margins and scrolling, creating an empty, immersive visual space.