I often debug responsive issues directly on my iPhone and need a lightweight Safari extension to make that practical. When switched on, it should let me tap any element and display a clear, color‑coded overlay of its CSS box model (margin, border, padding). A small control panel should offer quick presets to emulate popular mobile screen widths by adjusting the page’s viewport, so I can verify responsiveness in seconds. Please deliver it as a self-contained extension organized with an MVC pattern.