This example shows the proportion of smartphone app usage across six age groups using a horizontal stacked bar chart. The bars are divided into segments for social media, games, productivity, streaming, and other apps, with a color-coded legend for identification. The chart uses `d3.stack` to compute the stacked bar coordinates and `d3.scaleBand` for the age-group axis. It reads data from the CSV file `phones.csv` and renders the chart as an SVG element. Color assignments are made with `d3.scaleOrdinal`.