A grid of thin horizontal and vertical white strokes overlays the full browser window, but a circular mask reveals the pattern only within a central disc, creating a crisp boundary between the visible striped interior and a blank exterior. Built with D3.js (version 7.9.0) and rendered as SVG, the code uses `select`, `range`, and the `.join('rect')` API to generate 100 rects in each orientation. Two SVG masks—one with a white circle on black, the other inverted—alternately hide and reveal the respective stroke sets, producing the final composed image.