This example demonstrates a basic introduction to D3.js by creating a simple SVG scene with a red circle and a blue rectangle on a green canvas. The code uses D3 v7’s selection and append methods to build the SVG elements, setting their positions and fill attributes directly. It relies on the `d3.select` and `d3.attr` APIs to structure the visualization, serving as a minimal starting point for learning D3’s declarative syntax within an HTML page.