A bar chart displays a dataset of 20 values as vertically oriented rectangles, with each bar labeled by its numerical value. Hovering over a bar immediately changes its fill color to orange, while moving the mouse away triggers a smooth 250-millisecond transition that gradually restores the original blue color. The visualization uses D3.js version 4.5.0, specifically `d3.select`, `d3.scaleBand`, `d3.scaleLinear`, and the `transition` method with a `duration` parameter to animate the color changes.