This fork of the Billionaires D3 example displays a heatmap where each cell’s color intensity, using the Inferno interpolator via `d3.scaleSequential`, encodes a numeric value from a CSV file. The chart renders as an SVG with `d3.axisBottom` and `d3.axisLeft` for the categorical group and variable axes. Interactive tooltips are created with a `div` element and updated through `mouseover`, `mousemove`, and `mouseleave` events, showing the exact value of the hovered cell. The code uses D3 v6 and loads external data from GitHub.