Why migration requires care
Tailwind v4 introduced a CSS-first configuration model, automatic content detection improvements, a new engine and updated installation patterns. A v3 project should be migrated intentionally rather than replacing packages and hoping the old configuration behaves identically.
Major areas to review
Review the main CSS entry point, tailwind.config.js, PostCSS or Vite integration, custom plugins, content paths, theme extensions and any JavaScript-based configuration that maps to v4 CSS directives.
Compatibility exists
v4 provides @config and @plugin for compatibility in appropriate cases, allowing gradual migration. New customizations should generally use the v4 CSS-first model.
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