This bar chart visualizes COVID-19 cases across the top 20 countries, using horizontal bars to compare case counts. The visualization is built with React and D3 v5, where React manages state and renders SVG elements while D3 scales handle data mapping. The code uses `d3.scaleBand` for the categorical y-axis, `d3.scaleLinear` for the quantitative x-axis, and `d3.csv` to load the dataset from a GitHub gist. Tick marks and axis labels are generated manually through React's array mapping rather than using D3's axis components.