A donut chart visualizes a percentage value with a smooth animated transition, shifting the arc from zero to the given input over 750 milliseconds. The chart uses gradient colors that change based on the percentage range, from red for low values to green for high values. Hovering over the arc highlights it with a black stroke. The implementation uses D3 v5 with SVG rendering, leveraging `d3.arc`, `d3.interval`, and `transition.attrTween` for animation, alongside a linear gradient definition for color transitions.