This example shows a blank React + D3 visualization starter template with visible margin guides. The `VizContainer` component renders an SVG with an outer gray rectangle and inner light-gray rectangle to display the margin convention, using the `margin`, `innerWidth`, and `innerHeight` variables. The code imports React and ReactDOM directly via `React.createElement` and uses D3 v6 from a CDN. The `showMargins` prop toggles the guide rectangles, which can be removed by setting it to `false`. No data or chart elements are currently rendered.