Web Styling Tailwind

Tailwind CSS v4+ Patterns

Quick Guide: Tailwind CSS v4 uses CSS-first configuration with @import "tailwindcss" and @theme directive (NOT tailwind.config.js). Define design tokens as CSS variables in @theme, create custom utilities with @utility, custom variants with @custom-variant. Automatic content detection (no content array). Use @tailwindcss/vite for Vite, @tailwindcss/webpack for Webpack. All colors use oklch. v4.1 adds text shadows, masks, and input-device variants. No Sass/Less/Stylus support.

Detailed Resources:

• For code examples, see examples/ folder:
  • core.md - Setup, source detection, responsive design, dark mode, state variants, theme customization
  • advanced.md - Custom utilities, custom variants, container queries, 3D transforms, text shadows, masks, input-device targeting, animations, component extraction

CRITICAL: Before Using This Skill

All code must follow project conventions in CLAUDE.md (kebab-case, named exports, import ordering, import type, named constants)

(You MUST use @import "tailwindcss" and @theme for configuration - NEVER use tailwind.config.js, @tailwind base, or module.exports)

(You MUST use @utility for custom utilities - NEVER use @layer utilities {} (v3 syntax))

(You MUST use oklch or CSS variable references for custom colors in @theme - NEVER use hex/rgb for theme tokens)

(You MUST use @tailwindcss/vite for Vite, @tailwindcss/webpack for Webpack, @tailwindcss/postcss for others - NEVER use tailwindcss directly as PostCSS plugin)

(You MUST specify border colors explicitly - v4 defaults to currentColor not gray-200)

Auto-detection: Tailwind CSS, tailwindcss, @import "tailwindcss", @theme, @utility, @custom-variant, utility classes, bg-, text-, flex, grid, responsive design, dark:, hover:, focus:, @tailwindcss/vite, @tailwindcss/postcss, @tailwindcss/webpack, tailwind-merge, cn()

When to use:

• Styling with utility-first CSS classes directly in markup
• Configuring design tokens with CSS-first @theme directive
• Implementing responsive design with breakpoint variants
• Adding dark mode with dark: variant
• Creating custom utilities and variants in CSS
• Building component libraries with Tailwind utility classes
• Using container queries, 3D transforms, or modern CSS features

Key patterns covered:

• CSS-first setup with @import "tailwindcss" and @theme
• Responsive design with breakpoint variants (sm:, md:, lg:)
• Dark mode configuration (media, class, data-attribute strategies)
• State variants (hover:, focus:, group-*:, peer-*:)
• Theme customization with @theme namespaces
• Custom utilities with @utility and functional values
• Custom variants with @custom-variant
• Container queries (@container, @sm:, @max-*:)
• 3D transforms (rotate-x-*, perspective-*, transform-3d)
• Animation with @starting-style and @keyframes
• Text shadows, masks, overflow-wrap (v4.1)
• Component extraction with cn() (clsx + tailwind-merge)
• Migration notes from v3 to v4

When NOT to use:

• Projects requiring Sass/Less/Stylus (v4 is a standalone preprocessor, no Sass support)
• Projects needing IE11 or older browser support (requires Safari 16.4+, Chrome 111+, Firefox 128+)
• Tiny projects where a full utility framework is overkill (use plain CSS)
• Projects already using an established CSS Modules or CSS-in-JS design system

Philosophy

Tailwind CSS v4 follows a utility-first, CSS-native approach: style directly in markup using composable utility classes, configure design tokens in CSS with @theme, and extend with @utility/@custom-variant directives. No JavaScript configuration files needed.

Core Principles:

• Utility-first: Compose styles from small, single-purpose classes in HTML
• CSS-first configuration: Design tokens defined in CSS via @theme, not JavaScript
• Zero configuration defaults: Automatic content detection, sensible default theme
• Variant-driven states: Responsive, dark mode, hover, focus -- all via class prefixes
• Modern CSS foundation: Built on cascade layers, @property, color-mix(), oklch colors
• Performance-first: 5x faster full builds, 100x faster incremental rebuilds vs v3

v4 vs v3 -- Key Differences:

Core Patterns

Pattern 1: CSS-First Setup and Configuration

Tailwind v4 replaces JavaScript config with CSS-first configuration. Use @import "tailwindcss" instead of @tailwind directives, and @theme instead of tailwind.config.js.

Installation Options

Vite projects (recommended): Use @tailwindcss/vite for optimal performance. Webpack projects: Use @tailwindcss/webpack (added in v4.2). Other bundlers: Use @tailwindcss/postcss as PostCSS plugin. CLI: Use @tailwindcss/cli for standalone builds.

Key Concepts

• @import "tailwindcss" replaces the three @tailwind directives
• @theme defines design tokens that generate utility classes AND CSS variables
• @source adds paths not caught by automatic content detection
• @source not excludes paths from scanning (v4.1)
• @source inline("...") safelists specific utilities without source files (v4.1)
• @reference imports theme/utilities for scoped styles (Vue SFC, CSS Modules) without duplicating output
• No content array needed -- Tailwind auto-detects template files respecting .gitignore

For implementation examples, see examples/core.md.

Pattern 2: Responsive Design with Breakpoint Variants

Tailwind v4 uses mobile-first responsive design with breakpoint variants. Default breakpoints: sm (40rem), md (48rem), lg (64rem), xl (80rem), 2xl (96rem).

Key Concepts

• Mobile-first: base styles apply to all, breakpoint variants add overrides
• Custom breakpoints defined in @theme with --breakpoint-* namespace
• Stack breakpoints for ranges: md:max-lg:hidden (hide between md and lg)
• Use max-* variants for max-width queries: max-md:hidden

For implementation examples, see examples/core.md.

Pattern 3: Dark Mode

Tailwind v4 supports three dark mode strategies: media query (default), class-based toggle, and data-attribute toggle. Override the dark variant with @custom-variant.

Strategies

1. Media query (default): Uses prefers-color-scheme: dark -- zero config
2. Class-based: Add .dark class to <html> -- use @custom-variant dark
3. Data-attribute: Use data-theme="dark" -- use @custom-variant dark

Key Concepts

• Default dark mode works with system preference, no config needed
• For manual toggle, override the dark variant with @custom-variant
• Use (&:where(.dark, .dark *)) selector for class strategy
• Theme variables in @theme can reference CSS variables set by theme class

For implementation examples, see examples/core.md.

Pattern 4: State Variants

Tailwind v4 provides comprehensive state variants for interactive styling. The not-* variant is new in v4.

Available Variants

• Pseudo-classes: hover:, focus:, active:, visited:, first:, last:, odd:, even:, disabled:, required:, invalid:
• Group/Peer: group-hover:, group-focus:, peer-checked:, peer-invalid:
• Data attributes: data-[state=active]:, data-current:
• New in v4.0: not-hover:, not-focus:, inert:, starting: (for @starting-style)
• New in v4.1: pointer-fine:, pointer-coarse:, user-valid:, user-invalid:, noscript:, details-content:, inverted-colors:
• Container queries: @sm:, @md:, @lg:, @max-sm:

Key v4 Changes

• hover: only applies on devices with hover capability (no more mobile ghost hovers)
• not-* variant styles when condition is NOT met
• Variant stacking is left-to-right (CSS order): dark:hover:bg-gray-700

For implementation examples, see examples/core.md.

Pattern 5: Theme Customization with @theme

The @theme directive defines design tokens that generate both utility classes and CSS variables. Each namespace maps to specific utility types.

Namespaces

Key Concepts

• --color-*: initial resets all default colors before defining custom ones
• --*: initial resets the entire default theme
• @theme inline prevents CSS variable resolution issues when referencing other variables
• @theme static generates CSS variables even when utilities are unused
• @keyframes can be defined inside @theme for animation tokens

For implementation examples, see examples/core.md.

Pattern 6: Custom Utilities with @utility

The @utility directive replaces v3's @layer utilities {}. Supports static utilities, functional utilities with --value(), and modifiers with --modifier().

Types of Custom Utilities

1. Static: Fixed CSS declarations (@utility content-auto { content-visibility: auto; })
2. Functional: Accept values via --value() (@utility tab-* { tab-size: --value(integer); })
3. With modifiers: Optional modifiers via --modifier() for secondary values

Value Resolution

• --value(--namespace-*) matches theme variables
• --value(integer) matches bare integer values
• --value([length]) matches arbitrary values in brackets
• Multiple --value() declarations cascade (last match wins)

For implementation examples, see examples/advanced.md.

Pattern 7: Custom Variants with @custom-variant

The @custom-variant directive replaces v3's addVariant() plugin API. Define conditional styling rules in CSS. The @variant directive applies existing variants inline within CSS rules.

Syntax Forms

• @custom-variant shorthand: @custom-variant name (selector);
• @custom-variant block: @custom-variant name { /* rules with @slot */ }
• @variant (inline): @variant dark { /* styles */ } -- apply a variant inside custom CSS

For implementation examples, see examples/advanced.md.

Pattern 8: Container Queries

Container queries are built into v4 core (no plugin needed). Style elements based on container size, not viewport.

Key Concepts

• @container makes an element a query container
• @sm:, @md:, @lg: apply at container breakpoints (not viewport)
• @max-sm:, @max-md: for max-width container queries
• @min-md:@max-xl: for range queries
• Named containers with @container/name and @sm/name:

For implementation examples, see examples/advanced.md.

Pattern 9: 3D Transforms and Modern CSS

Tailwind v4 adds first-class 3D transform utilities and leverages modern CSS features.

3D Transform Utilities

• rotate-x-*, rotate-y-*, rotate-z-* for 3D rotation
• translate-z-* for depth translation
• scale-z-* for depth scaling
• perspective-* and perspective-origin-* for 3D perspective
• transform-3d to enable 3D transform context
• backface-hidden / backface-visible for card-flip effects

Other Modern Features

• @starting-style via starting: variant for enter/exit animations
• field-sizing-content for auto-resizing textareas
• color-scheme-dark for native dark mode scrollbars
• inset-shadow-* and inset-ring-* for layered box shadows
• text-shadow-* for text shadows with color/opacity support (v4.1)
• mask-* for gradient and image masking (v4.1)
• wrap-break-word / wrap-anywhere for overflow-wrap control (v4.1)
• --alpha() function for adjusting color opacity in custom CSS

For implementation examples, see examples/advanced.md.

Pattern 10: Component Class Composition with cn()

Use cn() (clsx + tailwind-merge) to handle class composition and conflict resolution. Compose utility classes programmatically when components need variants or overridable styles.

Key Concepts

• cn() combines clsx (conditional classes) with twMerge (conflict resolution)
• External className should always be last in cn() to allow consumer overrides
• Use variant objects for multi-variant components, cn() for simple composition
• Prefer cn() over @apply for component extraction (keeps utilities visible in code)

For implementation examples, see examples/advanced.md.

Decision Framework

When to Use Which Styling Approach

Need component variants (size, intent, state)?
|-- YES --> Variant objects + cn() + Tailwind classes
|-- NO --> Just utility classes in markup

Need custom utility not in Tailwind?
|-- YES --> Is it a single fixed style?
|   |-- YES --> @utility name { declarations }
|   |-- NO --> @utility name-* { --value() }
|-- NO --> Use built-in utilities

Need conditional styling based on parent/sibling state?
|-- YES --> Is parent state?
|   |-- YES --> group/group-* pattern
|   |-- NO --> peer/peer-* pattern
|-- NO --> Direct state variants (hover:, focus:)

Need responsive behavior based on...?
|-- Viewport size --> sm:/md:/lg: breakpoint variants
|-- Container size --> @container + @sm:/@md: variants
|-- Neither --> Static styling

Dark Mode Strategy

Is dark mode automatic (system preference only)?
|-- YES --> No config needed (default prefers-color-scheme)
|-- NO --> Need manual toggle?
    |-- YES --> Using class on <html>?
    |   |-- YES --> @custom-variant dark (&:where(.dark, .dark *))
    |   |-- NO --> @custom-variant dark (&:where([data-theme=dark], [data-theme=dark] *))
    |-- NO --> Default media query

Theme Customization Scope

Need to add a few custom tokens?
|-- YES --> Add to @theme alongside defaults

Need to replace an entire namespace?
|-- YES --> --namespace-*: initial; then define custom tokens

Need fully custom theme (no defaults)?
|-- YES --> --*: initial; then define everything

Need to share theme across projects?
|-- YES --> Create shared theme.css, import with @import

v3 to v4 Migration Decision

Is the project actively maintained?
|-- YES --> Does it use tailwind.config.js plugins?
|   |-- YES --> Can plugins be replaced with @utility/@custom-variant?
|   |   |-- YES --> Migrate to v4
|   |   |-- NO --> Keep v3 or use @config/@plugin compatibility
|   |-- NO --> Migrate to v4 (run npx @tailwindcss/upgrade)
|-- NO --> Stay on v3.4 (stable, still supported)

Integration Notes

Bundler Setup:

• Use @tailwindcss/vite for Vite-based projects (fastest)
• Use @tailwindcss/webpack for Webpack projects (v4.2+)
• Use @tailwindcss/postcss for other bundlers
• Use @tailwindcss/cli for standalone builds
• autoprefixer and postcss-import are NOT needed with v4

Component Integration:

• Use cn() for class composition and conflict resolution
• Forward className prop for consumer overrides
• Use tailwind-merge to resolve conflicting utility classes

What Tailwind Does NOT Replace:

• Complex CSS animations / @keyframes (use @theme for tokens, custom CSS for complex sequences)
• CSS variables for runtime values (use bg-(--my-var) arbitrary syntax)

RED FLAGS

High Priority Issues:

• Using tailwind.config.js without @config directive (v4 does NOT auto-detect JS config)
• Using @tailwind base; @tailwind components; @tailwind utilities; (v3 syntax, use @import "tailwindcss")
• Using @layer utilities {} for custom utilities (use @utility directive)
• Using tailwindcss directly as PostCSS plugin (use @tailwindcss/postcss)
• Using !flex important syntax (v4 uses flex! -- trailing not leading)
• Using bg-[--my-var] for CSS variables (v4 uses bg-(--my-var) with parentheses)
• Using hex/rgb colors in @theme (use oklch for P3 gamut support)
• Assuming border defaults to gray-200 (v4 defaults to currentColor)
• Assuming ring defaults to 3px (v4 defaults to 1px)

Medium Priority Issues:

• Using @apply for component extraction (use cn() with tailwind-merge instead -- keeps utilities visible)
• Not specifying @source for node_modules UI libraries (automatic detection skips node_modules)
• Using Sass/Less/Stylus with Tailwind v4 (not supported -- v4 is a standalone preprocessor)
• Using autoprefixer or postcss-import (not needed with v4)
• Using transform-none to reset transforms (v4 uses individual properties, use scale-none / rotate-0)

Common Mistakes:

• Forgetting @custom-variant dark when using class-based dark mode toggle
• Using content: ['./src/**/*.tsx'] (v4 auto-detects, no content array)
• Mixing v3 and v4 syntax in the same project
• Not running npx @tailwindcss/upgrade for automated migration

Gotchas and Edge Cases:

• Variant stacking order changed: v3 was right-to-left, v4 is left-to-right (follows CSS cascade)
• hover: only triggers on devices with hover capability (no phantom hover on touch devices)
• space-y-* / divide-* changed selectors: v3 used :not([hidden]) ~ :not([hidden]), v4 uses :not(:last-child) -- prefer gap-* with flex/grid
• Grid template values use underscores for spaces: grid-cols-[max-content_auto] (not commas)
• shadow-sm in v3 = shadow-xs in v4, shadow in v3 = shadow-sm in v4 (whole scale shifted)
• rounded-sm in v3 = rounded-xs in v4, rounded in v3 = rounded-sm in v4
• outline-none in v3 = outline-hidden in v4 (accessibility improvement)
• ring in v3 (3px) = ring-3 in v4 (default is now 1px)
• Browser requirements: Safari 16.4+, Chrome 111+, Firefox 128+ (no IE11, no older browsers)

CRITICAL REMINDERS

All code must follow project conventions in CLAUDE.md (kebab-case, named exports, import ordering, import type, named constants)

(You MUST use @import "tailwindcss" and @theme for configuration - NEVER use tailwind.config.js, @tailwind base, or module.exports)

(You MUST use @utility for custom utilities - NEVER use @layer utilities {} (v3 syntax))

(You MUST use oklch or CSS variable references for custom colors in @theme - NEVER use hex/rgb for theme tokens)

(You MUST use @tailwindcss/vite for Vite, @tailwindcss/webpack for Webpack, @tailwindcss/postcss for others - NEVER use tailwindcss directly as PostCSS plugin)

(You MUST specify border colors explicitly - v4 defaults to currentColor not gray-200)

Failure to follow these rules will produce v3 code that does not work with Tailwind CSS v4.

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