A blue rectangle and a text label reading "Follow Mouse" both track the cursor across an SVG canvas that fills the viewport. The page listens to mouse movement events and updates the x and y coordinates of both elements in real time. Built with D3 v7, the example uses selection methods like `append`, `attr`, and `on` to create and move the shapes. The SVG is sized to the browser window, and CSS hides page margins to maximize the tracking area.