A blank white canvas fills the browser viewport, rendered as a single rounded rectangle. The visualization demonstrates a minimal starting point for D3-based projects, showing an empty SVG surface with no data or interactive elements. The code uses D3 v5's `select` function to access the SVG element, reads its width and height attributes, and appends a `rect` with a 40-pixel corner radius using `svg.append`. A fixed-position CSS body ensures the canvas remains centered and non-scrollable.