This example visualizes valence and arousal data across epochs 90-180 using two overlaid SVG line charts with yellow axes and a blue-to-red gradient stroke. The arousal chart displays a thin line with clickable circles that show tooltips, while the valence chart uses a thicker gradient line. Both charts load CSV data via `d3.csv`, scale axes with `d3.scaleLinear`, and render paths using `d3.line`. The visualization demonstrates D3 v4 imports, local ES6 modules, and interactive tooltip behavior on a black background.