A full-screen SVG canvas displays only a rounded rectangle drawn with D3's `select` and `append`. The rectangle fills the viewport dimensions, which are read from `document.body.clientWidth` and `clientHeight`. The visualization uses a minimal blank state with no explicit data source; the code sets the SVG's width and height attributes and applies a 40-pixel corner radius via `attr('rx', 40)`. No additional interactions or updates occur, leaving a static, empty composition.