Source code in 15 libraries — Python: Altair, Bokeh, lets-plot, Matplotlib, Plotly, plotnine, Pygal, Seaborn; R: ggplot2; Julia: Makie.jl; JavaScript: Chart.js, D3.js, Apache ECharts, Highcharts, MUI X Charts.
A stacked area chart normalized to 100%, where each area represents the percentage contribution of a category to the total. The combined height always equals 100%, showing proportional changes over time.

Preview render from the ggplot2 implementation.