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+# Tailwind CSS v3 to v4 Migration Guide
+
+This guide documents the process for upgrading VibeTunnel from Tailwind CSS v3 to v4.
+
+## Current Status
+
+VibeTunnel currently uses Tailwind CSS v3.4.17 (see `web/package.json:152`).
+
+## Prerequisites
+
+- **Node.js 20 or higher** - The upgrade tool requires Node.js 20+
+- **Clean git branch** - Always run the migration in a new branch
+- **All changes committed** - Ensure your working directory is clean
+
+## Automated Migration
+
+Tailwind provides an automated upgrade tool that handles most of the migration:
+
+```bash
+cd web
+npx @tailwindcss/upgrade@next
+```
+
+### What the Tool Does
+
+The upgrade tool automatically:
+- Updates dependencies to v4
+- Migrates `tailwind.config.js` to CSS format
+- Updates template files for breaking changes
+- Converts deprecated utilities to modern alternatives
+- Updates import statements
+
+### Important Notes
+
+- The tool only works on v3 projects. If you've partially upgraded, it will refuse to run
+- To re-run after a partial upgrade, first reinstall v3: `npm install tailwindcss@3`
+- Run in a new git branch to easily review changes
+- Expect to spend 2-4 hours on migration for a medium project
+
+## Major Changes in v4
+
+### 1. CSS Import Syntax
+
+**Before (v3):**
+```css
+@tailwind base;
+@tailwind components;
+@tailwind utilities;
+```
+
+**After (v4):**
+```css
+@import "tailwindcss";
+```
+
+### 2. Configuration Changes
+
+- `tailwind.config.js` is no longer needed
+- Configuration moves to CSS using `@theme` and `@plugin` directives
+- Zero-config by default - just import and start using
+
+### 3. Plugin Installation
+
+**Before (v3):**
+```js
+// tailwind.config.js
+module.exports = {
+  plugins: [
+    require('@tailwindcss/typography'),
+    require('@tailwindcss/forms'),
+  ]
+}
+```
+
+**After (v4):**
+```css
+@import "tailwindcss";
+@plugin "@tailwindcss/typography";
+@plugin "@tailwindcss/forms";
+```
+
+### 4. Dark Mode Configuration
+
+**Default:** Uses `prefers-color-scheme` media query
+
+**For class-based dark mode:**
+```css
+@import "tailwindcss";
+@custom-variant dark (&:where(.dark, .dark *));
+```
+
+### 5. PostCSS Changes
+
+The PostCSS plugin moved to a separate package:
+```bash
+npm install @tailwindcss/postcss
+```
+
+Update your PostCSS config to use the new package.
+
+## Breaking Changes
+
+### Removed Utilities
+
+Deprecated v3 utilities have been removed. The upgrade tool handles replacements automatically.
+
+### CSS Variable Syntax
+
+**Before (v3):**
+```html
+<div class="bg-[--my-color]">
+```
+
+**After (v4):**
+```html
+<div class="bg-(--my-color)">
+```
+
+### Container Queries
+
+Container queries are now built-in. Remove `@tailwindcss/container-queries` plugin.
+
+### Renamed Scales
+
+Default shadow, radius, and blur scales renamed for consistency. The upgrade tool handles this.
+
+## Limitations
+
+### SCSS/Sass Files
+
+- The upgrade tool doesn't support `.scss` or `.less` files
+- v4 isn't compatible with Sass/SCSS syntax
+- Consider migrating to plain CSS (v4 supports native CSS nesting)
+
+### Complex Configurations
+
+Some complex configurations may need manual migration:
+- Custom plugins with complex logic
+- Advanced theme extensions
+- Non-standard build setups
+
+## Migration Checklist
+
+1. **Preparation**
+   ```bash
+   # Ensure Node.js 20+
+   node --version
+   
+   # Create new branch
+   git checkout -b upgrade-tailwind-v4
+   
+   # Ensure clean working directory
+   git status
+   ```
+
+2. **Run Migration**
+   ```bash
+   cd web
+   npx @tailwindcss/upgrade@next
+   ```
+
+3. **Review Changes**
+   - Check git diff carefully
+   - Look for any migration warnings
+   - Review updated import statements
+
+4. **Test Thoroughly**
+   ```bash
+   # Start development server
+   pnpm run dev
+   
+   # Run quality checks
+   pnpm run check
+   ```
+
+5. **Manual Fixes**
+   - Address any remaining warnings
+   - Update custom plugins if needed
+   - Fix any styling issues
+
+6. **Verify Production Build**
+   ```bash
+   pnpm run build
+   ```
+
+## Performance Benefits
+
+v4 brings significant performance improvements:
+- **5x faster** full builds
+- **100x faster** incremental builds (measured in microseconds)
+- Smaller CSS output
+- Better tree-shaking
+
+## Alternative Tools
+
+**TWShift** - AI-powered migration tool for complex configurations:
+- Better handling of complex themes
+- Keyframes and animations support
+- Advanced plugin migration
+- Available at: https://twshift.com/
+
+## Rollback Plan
+
+If issues arise:
+1. Keep the migration branch separate until fully tested
+2. Can always revert to v3 by switching branches
+3. v3.4 will continue to receive security updates
+
+## Resources
+
+- [Official Upgrade Guide](https://tailwindcss.com/docs/upgrade-guide)
+- [Tailwind CSS v4 Announcement](https://tailwindcss.com/blog/tailwindcss-v4)
+- [Migration Discussions](https://github.com/tailwindlabs/tailwindcss/discussions)
+
+## Browser Support
+
+v4 requires:
+- Safari 16.4+
+- Chrome 111+
+- Firefox 128+
+
+If you need older browser support, stay on v3.4.
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