Voronoi Overlay with Labels
A multi-line chart displays cumulative COVID-19 deaths over time for multiple countries, with a logarithmic y-axis. A Voronoi overlay, built with `d3.Delaunay`, captures mouse hover events across the chart area, highlighting the nearest data point and its corresponding line. A tooltip with country name, death count, and date follows the cursor, while the active series is emphasized. Data comes from the CSSE COVID-19 time series, rendered as SVG in React using d3 scales and axes.