A theme river displays the moving average of house property sales prices over time, broken down by property type and bedroom count. The visualization uses a silhouette offset to stack the series symmetrically around a central axis, highlighting each category's contribution. Users can drag and drop colored blocks to reorder the legend, which triggers an immediate redraw of the stacked areas via `d3.stack` and `d3.area`. The chart is built with `d3.csv`, `moment.js` for date parsing, and SortableJS for interactive reordering.