This example demonstrates a multi-series line chart comparing sales, profit, and expense data across 150 synthetic data points. The chart uses D3.js v7 to generate random values for each series, which are then plotted as three distinct colored lines using `d3.line()` and `d3.scaleLinear()` scales. The visualization includes axis labels, a title, and a manual legend, all rendered as SVG elements within a single `<svg>` container. The code explicitly handles margin calculations and applies `d3.axisBottom()` and `d3.axisLeft()` for axis generation.