This example demonstrates the D3 margin convention, a reusable pattern for structuring SVG charts with explicit padding around the plotting area. A component function applies the margin to an SVG, translating a container `g` element and returning the computed inner dimensions. It then renders a single rounded rectangle that fills this inner space, resizing dynamically on window resize events. The code uses D3 v5’s selection methods, including `merge` for efficient updates, and a custom `marginConvention` helper for managing layout.