This example demonstrates how to build custom legends for both ordinal color scales and quantitative size scales using D3 v5 within a React application. The color legend maps fruit categories (apple, lemon, lime, orange) to corresponding colors, while the size legend uses `scaleSqrt` to represent numeric values from 0 to 10 with proportional circle radii. Both legends employ the general update pattern with data joins on SVG groups, using `selection.enter()`, `merge()`, and `exit()` to handle dynamic updates. The code also showcases `sizeScale.ticks()` to generate clean tick values for the size legend.