This example shows a round slider built with D3.js, where a draggable handle moves along a circular track to represent a value. The visualization renders an SVG circle as the slider’s circumference and a small draggable dot that users can click and pull around the ring. The code uses D3’s `d3.drag` and `d3.event` to handle pointer interactions, calculating the handle’s position via trigonometric functions (`Math.acos`, `Math.sin`, `Math.cos`) based on its distance from the center. The slider’s state is stored in a simple data array, and the handle’s color changes from steelblue to red while dragging, as defined in the accompanying CSS.