This example displays two mirrored stacks of seven concentric circles, each with a distinct rainbow hue and uniform 0.7 opacity, on a green background. Using D3.js v7, the code binds an array of circle objects to SVG elements via `selectAll().data().join()`, setting each circle's position, radius, and fill color. The visualization is rendered inside a fixed full-viewport container, with dimensions derived from `container.clientWidth` and `container.clientHeight`.