This fork demonstrates D3 selection and transition behavior through a single animated circle that moves across an SVG canvas, changing fill color to random HSL hues. The visualization shows how the `transition()` API with `duration` and `ease` methods creates bouncy and smooth movement, cycling through a continuous loop. The code uses `d3.select` to append the SVG and circle elements, `transition.attr` to animate position and color, and exports reusable data-generation functions from `makeData.js` and `vizData.js`. The example renders via SVG with animation, built using D3 v6.6.2.