Migrating From V3

Migrating from v3 to v4

Purpose

Migrate existing Tailwind CSS v3 projects to v4's CSS-first configuration, updated utilities, and modern color system.

Automated Migration Tool

Tailwind provides an automated upgrade tool:

npx @tailwindcss/upgrade@next

Requirements:

• Node.js 20 or higher
• Run in a new git branch
• Review all changes manually
• Test thoroughly

What it handles:

• Updates dependencies
• Migrates configuration to CSS
• Updates template files
• Converts utility class names

What it doesn't handle:

• Custom plugins (manual migration needed)
• Complex configuration logic
• Dynamic class generation

Configuration Migration

JavaScript Config → CSS Theme

v3 (tailwind.config.js):

module.exports = {
  content: ['./src/**/*.{html,js}'],
  theme: {
    extend: {
      colors: {
        brand: '#3b82f6',
        accent: '#a855f7',
      },
      fontFamily: {
        sans: ['Inter', 'sans-serif'],
        display: ['Satoshi', 'sans-serif'],
      },
      spacing: {
        18: '4.5rem',
        72: '18rem',
      },
      borderRadius: {
        '4xl': '2rem',
      },
    },
  },
  plugins: [],
};

v4 (CSS @theme):

@import 'tailwindcss';

@theme {
  --font-sans: 'Inter', sans-serif;
  --font-display: 'Satoshi', sans-serif;

  --color-brand: oklch(0.65 0.25 270);
  --color-accent: oklch(0.65 0.25 320);

  --spacing-18: 4.5rem;
  --spacing-72: 18rem;

  --radius-4xl: 2rem;
}

Content Detection

v3:

content: ['./src/**/*.{html,js,jsx,ts,tsx}']

v4:

Automatic detection. No configuration needed.

Manual control (if needed):

@import 'tailwindcss';
@source "../packages/ui";
@source not "./legacy";

Import Syntax Changes

v3:

@tailwind base;
@tailwind components;
@tailwind utilities;

v4:

@import 'tailwindcss';

Utility Class Renames

Opacity Modifiers

v3:

<div class="bg-black bg-opacity-50"></div>
<div class="text-gray-900 text-opacity-75"></div>
<div class="border-blue-500 border-opacity-60"></div>

v4:

<div class="bg-black/50"></div>
<div class="text-gray-900/75"></div>
<div class="border-blue-500/60"></div>

Migration pattern:

• bg-opacity-{value} → bg-{color}/{value}
• text-opacity-{value} → text-{color}/{value}
• border-opacity-{value} → border-{color}/{value}

Flex Utilities

v3:

<div class="flex-shrink-0"></div>
<div class="flex-shrink"></div>
<div class="flex-grow-0"></div>
<div class="flex-grow"></div>

v4:

<div class="shrink-0"></div>
<div class="shrink"></div>
<div class="grow-0"></div>
<div class="grow"></div>

Migration pattern:

• flex-shrink-* → shrink-*
• flex-grow-* → grow-*

Shadow Utilities

v3:

<div class="shadow-sm"></div>

v4:

<div class="shadow-xs"></div>

Migration:

• shadow-sm → shadow-xs
• All other shadow utilities remain the same

Ring Width

v3 default:

<input class="ring" />

Ring width: 3px

v4 default:

<input class="ring" />

Ring width: 1px

To keep v3 behavior:

<input class="ring-3" />

Color System Changes

Default Border and Ring Colors

v3:

<div class="border"></div>

Border color: gray-200

v4:

<div class="border"></div>

Border color: currentColor

To keep v3 behavior:

<div class="border border-gray-200"></div>

OkLCh Color Space

v3 (RGB):

colors: {
  brand: '#3b82f6',
}

v4 (OkLCh):

@theme {
  --color-brand: oklch(0.65 0.25 270);
}

Use conversion tool: https://oklch.com/

PostCSS Configuration

Plugin Changes

v3:

module.exports = {
  plugins: {
    'tailwindcss': {},
    'autoprefixer': {},
  },
};

v4:

export default {
  plugins: {
    '@tailwindcss/postcss': {},
  },
};

No longer need autoprefixer or postcss-import.

Vite Plugin

v3:

import tailwindcss from 'tailwindcss';
import autoprefixer from 'autoprefixer';

export default defineConfig({
  css: {
    postcss: {
      plugins: [tailwindcss(), autoprefixer()],
    },
  },
});

v4:

import tailwindcss from '@tailwindcss/vite';

export default defineConfig({
  plugins: [tailwindcss()],
});

Preflight Changes

Placeholder Colors

v3:

Placeholder text: gray-400

v4:

Placeholder text: currentColor at 50% opacity

To keep v3 behavior:

@layer base {
  ::placeholder {
    color: theme('colors.gray.400');
  }
}

Button Cursor

v3:

button {
  cursor: pointer;
}

v4:

button {
  cursor: default;
}

To restore v3 behavior:

@layer base {
  button {
    cursor: pointer;
  }
}

Feature Additions

Built-in Container Queries

v3 (plugin required):

plugins: [require('@tailwindcss/container-queries')]

v4 (built-in):

No plugin needed. Use @container and @{breakpoint}: syntax.

3D Transforms

v3:

Not available

v4:

<div class="transform-3d rotate-x-45 rotate-y-30 translate-z-12"></div>

Starting Variant for Animations

v3:

Not available

v4:

<div class="opacity-100 starting:opacity-0 transition-opacity"></div>

Breaking Changes Checklist

• Update dependencies to v4
• Migrate tailwind.config.js to @theme
• Replace @tailwind directives with @import
• Update PostCSS configuration
• Convert opacity utilities (bg-opacity → bg-{color}/{value})
• Rename flex utilities (flex-shrink → shrink)
• Update shadow-sm to shadow-xs
• Add explicit border colors if using bare border
• Update ring-3 if expecting 3px default
• Convert hex colors to oklch()
• Remove container-queries plugin (now built-in)
• Test placeholder colors
• Test button cursor behavior
• Update arbitrary value syntax (spaces → underscores)

Migration Strategy

Phase 1: Preparation

1. Create new git branch
2. Ensure all changes committed
3. Run automated migration tool
4. Review generated changes

Phase 2: Configuration

1. Convert tailwind.config.js to CSS @theme
2. Update PostCSS/Vite configuration
3. Replace @tailwind directives
4. Add @source if needed

Phase 3: Utilities

1. Search and replace opacity modifiers
2. Rename flex utilities
3. Update shadow utilities
4. Add explicit border colors
5. Convert hex colors to oklch()

Phase 4: Testing

1. Test all pages/components
2. Verify responsive behavior
3. Check dark mode
4. Test interactive states
5. Validate production build

Phase 5: Cleanup

1. Remove unused dependencies
2. Delete tailwind.config.js
3. Update documentation
4. Commit changes

Common Issues

Styles Not Applying

Check:

1. CSS import: @import "tailwindcss";
2. PostCSS plugin: @tailwindcss/postcss
3. Vite plugin: @tailwindcss/vite
4. Template files not in .gitignore

Class Names Not Working

Ensure:

1. Class names are complete strings
2. Not using dynamic concatenation
3. Using underscores for spaces in arbitrary values

Colors Look Different

OkLCh uses different color space. Convert hex to oklch using: https://oklch.com/

Build Errors

Check:

1. Node.js version (20+)
2. Dependencies updated
3. PostCSS config using correct plugin

See Also

• references/breaking-changes.md - Complete breaking changes list
• references/migration-checklist.md - Step-by-step migration guide