This example shows a red square with a thick black border rendered inside an SVG canvas, demonstrating basic D3.js DOM manipulation. The code uses `d3.selectAll('svg')` to target the SVG element and appends a `rect` with attributes for position, size, stroke, and fill. It relies on the D3 v5 library loaded from a CDN, and renders the shape as pure SVG geometry without any data binding or interaction. The result is a static visual, illustrating how D3 can directly create and style SVG elements.