A bubble chart displays countries as circles positioned by GDP per capita (x-axis) and life expectancy (y-axis), with circle size encoding population. Each bubble is colored by continent, drawn as SVG circles using `d3.forceSimulation` with custom forces for positioning. The code loads data from a JSON array and uses `d3-scale-chromatic` for categorical color mapping. Hovering a bubble changes its stroke from white to black via CSS.