This stacked bar chart visualizes population by country, segmented across multiple religions. Built with React and D3.js, it uses `d3.layout.stack` and `d3.scale.ordinal` to construct the bars, with SVG rendering for crisp graphics. Interactive tooltips via `d3-tip` reveal precise values on hover, while a legend (using `d3.legend`) triggers a responsive overlay effect that highlights bars from a selected religion and dims others via animated transparency transitions.