Currently, the web target uses a fixed window size and it sizes the canvas based on it. It would be nice to instead have a mode that allows the canvas to be laid out on the page with CSS layout like flexbox or CSS grid. The resizing of the element can be detected using ResizeObsever, which can also handle pixel-perfect canvas sizing (#1659 (comment)). In this mode, the winit window should not be resizable by user code.