This example shows a single, animated pie chart where the foreground arc transitions to a new random angle every 1.5 seconds, with the background arc remaining fixed at 100%. Built with D3 v5, it renders two SVG path arcs using a custom `d3.arc` generator with bound inner and outer radii. The animation is driven by `d3.interval` and `transition.attrTween`, which interpolates the `endAngle` value in data space before computing the new path string, ensuring smooth angular transitions.