This example shows an animated donut chart that displays a percentage value at its center and updates its arc and color gradient automatically. The chart visualizes a data array where the third element (80%) drives the arc length and determines a six-stop linear gradient color scheme ranging from red to green based on the value. Built with D3 v5 and React, it uses `d3.arc` for the donut geometry, `transition.attrTween` with an interpolator to smoothly animate the arc between states, and a toggle button to switch between two datasets. The SVG rendering includes a static gray background arc and a foreground path filled via a dynamically configured `linearGradient`.