This example shows an area chart of visual acuity data, with a gradient fill transitioning from green through yellow to red based on y-values. The chart encodes data points as white circles positioned along the area’s upper boundary, each with a title tooltip displaying its value. Built with D3 v5, the visualization uses `d3.scaleLinear` for both x/y positioning and color mapping, an `area()` generator with `curveMonotoneX` for the shape, and SVG `linearGradient` definitions to color the fill. A simple SVG rect outlines the plot area.