This example displays a React line chart tracking cumulative global COVID-19 deaths over time, using data from the Johns Hopkins Coronavirus dataset. The chart renders as an SVG, with the line path generated by `d3.line()` and scales created via `scaleTime()` and `scaleLinear()`. Red marker lines highlight the current date and the three-million-death threshold, with the YMarkerLine and XMarkerLine components positioned using the scales. Axes are drawn with `axisBottom()` and custom React components that leverage `useRef` and `useEffect` to integrate D3 selections into the React lifecycle.