A blank SVG canvas fills the browser window, framed by a single rounded rectangle. The example demonstrates a minimal setup for web-based visualization, using D3 v6 to select the SVG element and set its dimensions based on the viewport. The code imports `select` and `arc` from D3, though only `select` is used to append the background shape. Styling is handled externally via CSS, which fixes the body and hides overflow to ensure the canvas remains visually clean and uncluttered.