A small multiple bar chart displays the population structure of Uruguay in 1950, comparing six categories (A–F) against a 0–100 scale. A yellow button triggers an animated transition using `rects.transition().duration(1000)` to update bar heights to a second dataset (val2), while the title text changes to "Population structure of Uruguay, 2015 (%)". The chart is rendered as SVG using `d3.axisBottom` and `d3.axisLeft` for axes, with data defined inline from a gist source.