This example builds an interactive smiley face using React and D3 v5. The page loads a CSS named color dataset from a GitHub gist and displays its file size, row count, and column count in a text overlay. A single circle follows the mouse position across the full window, rendering via SVG elements managed through React state and event handlers. The visualization demonstrates React’s `useState` and `useCallback` hooks for responsive, real-time updates, with D3’s `csv` method fetching and parsing the external data.