This area chart displays the relationship between horsepower and miles per gallon for a set of cars, with a filled green region showing how MPG decreases as horsepower increases. The visualization loads a CSV file from GitHub using `d3.csv`, converts the numeric fields, and sorts the data by horsepower. It uses `d3.scaleLinear` for both axes, `d3.area` to generate the filled path, and `d3.axisBottom` and `d3.axisLeft` to render the coordinate axes. The SVG output is styled with CSS for a clean presentation.