Lay the styling foundation on Tailwind v4. styles/theme.css holds every token from design-reference under Tailwind's namespaces, with Tailwind's own palette, scales, and breakpoints cleared so utilities can only name the theme, and styles/base.css styles only the document. Main's stand-in look moves to styles/legacy.css, in a layer between the base and the utilities, scoped to stop at any area marked data-ported and restoring the browser defaults Preflight removes, until the port is done. A System, Light, or Dark choice is kept on the device and applied by a script in the head before the first paint, and useInstantThemeSwitch switches without smearing for the system and other tabs. The icons come over from design-reference taking a class, the logo draws inline in theme colors from the favicon's file, cn merges classes knowing the theme's names, Biome sorts classes, and a test keeps raw colors and lengths out of components.