This example shows the average monthly temperature in degrees Celsius as a smooth area chart, with a tooltip that displays the month and exact temperature when a data point is hovered. The chart is built using D3 version 7 and renders as an SVG, with points drawn as circles that change color and size on hover. The code uses `d3.scaleBand` for the categorical month axis, `d3.scaleLinear` for the temperature axis, and `d3.area` to generate the filled path. Tooltip positioning relies on `event.pageX` and `event.pageY`.