A blank SVG canvas is filled with a single gray rectangle that spans the full width and height of the viewport, creating a minimalist visual effect. The example demonstrates the basic structure of a D3.js v5 project, using `d3.select` to access the SVG element and `svg.append` to add a `rect` element. The rectangle’s width is set twice in the code, while its height remains unspecified, leaving the shape incomplete. This serves as a starting point for understanding SVG rendering with D3’s declarative API.