A stacked bar chart visualizes device usage proportions across five age groups, sourced from CSV data. It reveals how smartphone reliance decreases with age while tablet, laptop, and desktop usage generally increases. Built with D3 v7, the chart uses SVG rendering, a linear x-scale for percentages, a band y-scale for age categories, and an ordinal color scale. The stacked layers are created via `d3.stack()`, with tooltips showing exact percentages, and axes are formatted using `d3.axisBottom` and `d3.axisLeft`.