Tailwind CSS v4.1 Core

Documentation

• theme.md - CSS theme variables, design tokens, customization
• functions-and-directives.md - @utility, @variant, @theme, @apply
• adding-custom-styles.md - Custom utilities and variants
• detecting-classes-in-source-files.md - Content detection
• upgrade-guide.md - Migration from v3 to v4

Quick Reference - @theme Namespaces

Configuration CSS-first

Before (v3)

// tailwind.config.js
module.exports = {
  theme: {
    extend: {
      colors: { brand: '#3B82F6' }
    }
  }
}

After (v4)

@import "tailwindcss";

@theme {
  --color-brand: #3B82F6;
}

Directives v4

@utility - Create a utility

@utility tab-4 {
  tab-size: 4;
}
/* Usage: class="tab-4" */

@variant - Conditional style

.card {
  @variant dark {
    background: #1a1a2e;
  }
}

@custom-variant - New variant

@custom-variant dark (&:where([data-theme="dark"], [data-theme="dark"] *));
/* Usage: dark:bg-gray-900 */

v3 → v4 Breaking Changes

Removed @tailwind directives

/* v3 */
@tailwind base;
@tailwind components;
@tailwind utilities;

/* v4 */
@import "tailwindcss";

Renamed utilities

Removed deprecated utilities

• bg-opacity-* → use bg-black/50
• text-opacity-* → use text-black/50
• flex-shrink-* → use shrink-*
• flex-grow-* → use grow-*

Custom utilities syntax

/* v3 */
@layer utilities {
  .tab-4 {
    tab-size: 4;
  }
}

/* v4 */
@utility tab-4 {
  tab-size: 4;
}

Variables in arbitrary values

<!-- v3 -->
<div class="bg-[--brand-color]"></div>

<!-- v4 -->
<div class="bg-(--brand-color)"></div>

Important modifier position

<!-- v3 -->
<div class="!bg-red-500">

<!-- v4 -->
<div class="bg-red-500!">

Upgrade Tool

npx @tailwindcss/upgrade

Requires Node.js 20+

Browser Support

• Safari 16.4+
• Chrome 111+
• Firefox 128+

Installation

npm install -D tailwindcss @tailwindcss/postcss
# or for Vite
npm install -D @tailwindcss/vite
# or for CLI
npm install -D @tailwindcss/cli

Core API Functions

--alpha()

Adjust color opacity:

color: --alpha(var(--color-lime-300) / 50%);

--spacing()

Generate spacing values:

margin: --spacing(4);

@apply

Inline utility classes:

.btn {
  @apply px-4 py-2 rounded-lg font-bold;
}

Key Resources

• Official Theme Variables Documentation
• @theme Directive Syntax
• Content Detection Configuration
• Custom Variant Creation
• Animation Keyframes Definition
• CSS Variables Usage