This example displays a choropleth-style regional map of Swedish counties, rendered as an SVG using React and D3 v5. It shows the geographic boundaries of each county filled with a teal color, while interior borders are highlighted with a lighter stroke. The code loads TopoJSON data from a GitHub gist, converts it to GeoJSON using `topojson.feature` and `topojson.mesh`, and projects it with `d3.geoMercator` fitted to the viewport via `projection.fitExtent`. Paths are drawn using the `d3.geoPath` generator.