The area chart displays daily average air temperature variations in Belgium for 2021, plotted as a smooth line over time. Built with D3 v6, the visualization uses an SVG rendering approach with a linear gradient for the line color and a red fill for the area beneath the curve. The code imports `csv`, `scaleTime`, `scaleLinear`, `axisBottom`, `axisLeft`, `curveBasis`, and `line` APIs to fetch and process the data, construct the axes with grid lines, and generate the smoothed path. The resulting chart includes labeled axes for months and temperature, with a title, all styled via a separate CSS file.