This example uses React and D3 to create a full-window SVG grid of horizontal and vertical stripes. A pair of circular SVG masks selectively reveals the underlying patterns: one circle is punched out of a white rectangle to show the vertical stripes, while a second white circle exposes the horizontal stripes. The code builds the masks and rectangles imperatively via D3's `select` and `join`, with `range` generating the stripe positions. The result is a simple, mask-driven optical illusion where the two stripe directions appear only within their respective circular regions.