This example demonstrates D3’s margin convention by rendering a horizontal bar chart of UN population data for the top ten countries in 2020. The chart uses React state to load the CSV via `d3.csv` and maps each country to a `<rect>` inside a translated `<g>` element, with scales from `d3.scaleBand` and `d3.scaleLinear`. All marks are drawn as SVG within a fixed 960×500 viewport, clearly separating the plotting area from the surrounding margins.