A playful set of five text elements counts up to 10 on load with staggered delays, then changes to 50 on mouseenter and back to 10 on mouseleave using `d3.transition` and `d3.interpolateRound` inside a custom `.tween`. The page background animates from red to green via a chained `transition().style()`, while an SVG renders six yellow circles with radii proportional to the square root of their data values using `d3.selectAll().data().enter().append()`. The example demonstrates D3 v7’s selection, transition, and tweening APIs in a plain HTML page.