A stacked bar chart displays population distribution across seven age groups for each US state, using data from a local CSV file. The chart employs D3 v7’s `d3.stack`, `d3.scaleBand`, `d3.scaleLinear`, and `d3.scaleOrdinal` to render SVG rectangles. Hovering over a bar segment triggers a tooltip showing the state, age group, and exact population value, implemented via mouseover and mouseout events with CSS-styled tooltip divs.