A blank, interactive canvas fills the browser window, rendered as a single rounded rectangle spanning the full viewport. The example demonstrates a minimal setup for a D3.js visualization, using `d3.select` to target the SVG element and setting its dimensions based on the document body's client width and height. The code imports `select` and `arc` from D3 v5, though the latter is not used here. The SVG background is drawn via `.append('rect')`, with the page's fixed positioning and margin removal handled by the accompanying CSS file.