This example displays the Keeling Curve, a record of atmospheric CO2 measurements over time, as a responsive line chart. The chart updates its dimensions to fit its container, thanks to the `observeResize` and responsive axes libraries. The `viz` function uses `d3.scaleTime` and `d3.scaleLinear` to map dates and CO2 values, and `d3.line` to generate the path. The plot includes a light gray inner rectangle and semi-transparent circles, though the circle layer is not visible in this configuration.