This example presents two linked visualizations of a sleep health dataset: a multi-series line chart and a combined chart. The line chart plots Age against Sleep Duration, Stress Level, and Daily Steps using d3.line with d3.scaleLinear axes, while colored dots and tooltips show exact values. The combined chart reuses the same scales and color encoding to display the data differently. The code loads data via d3.csv, applies SVG rendering, and includes interactive mouseover events with tooltip transitions.