A full-screen SVG is constructed entirely with native DOM methods via `document.createElementNS`, without any external libraries. It draws 100 horizontal blue rectangles, each 10 pixels tall, stacked vertically across the viewport. A circular mask with a 200-pixel radius, centered on the screen, restricts visibility to a round window showing a portion of the stripes. The mask uses a white-filled circle, and every rectangle references this mask through its `mask` attribute, creating a simple geometric pattern reminiscent of a flag.