name: tailwindcss
description: Tailwind CSS v4 patterns for styling Next.js applications. This skill should be used when styling components, creating responsive layouts, implementing design systems, or working with custom utilities. Covers v4-specific CSS-first configuration with @theme/@import/@utility directives, design tokens, responsive patterns, mobile-first design, and Atlas-specific conventions including 8px grid spacing system and accessibility patterns.

Tailwind CSS v4

Purpose

Provide comprehensive Tailwind CSS v4 styling patterns for Next.js applications using the modern CSS-first configuration approach. Emphasize utility-first design, mobile-first responsive patterns, 8px grid alignment, and accessibility-first principles aligned with Atlas design system.

When To Use This Skill

Component Styling:
- Apply Tailwind utility classes to new components
- Create responsive layouts using flexbox and grid
- Implement spacing using 8px grid system
- Style interactive states (hover, focus, active, disabled)

Design System Implementation:
- Define custom design tokens using @theme directives
- Configure color palettes with semantic names
- Set up typography scales and font families
- Create custom utilities with @utility directive
- Implement dark mode support

Responsive Design:
- Build mobile-first responsive patterns
- Apply breakpoint-specific utilities (sm:, md:, lg:, xl:)
- Create adaptive layouts that work across devices
- Ensure 44px minimum touch targets for mobile (WCAG AAA)

Accessibility:
- Add proper focus states with focus-visible
- Ensure sufficient color contrast ratios
- Hide decorative elements from screen readers (sr-only)
- Implement keyboard-navigable interfaces

Migration & Troubleshooting:
- Convert Tailwind v3 syntax to v4 CSS-first approach
- Debug configuration issues with @theme and @import
- Resolve spacing inconsistencies
- Fix accessibility violations (missing focus rings, low contrast)

Overview

Tailwind CSS v4 introduces a CSS-first configuration approach that moves theme customization from JavaScript config files into CSS using @theme, @import, and @utility directives. This skill emphasizes:

1. Utility-First Design: Compose UI from small, single-purpose classes
2. Mobile-First Responsive: Start with base styles, add breakpoint variants
3. Design System Alignment: Use semantic tokens and 8px grid system
4. Accessibility First: Focus states, contrast, screen reader support
5. V4 Modern Syntax: CSS-first configuration, custom utilities

Core Principles

Utility-First Composition:

<div className="flex items-center gap-4 p-6 bg-white rounded-lg shadow">

Mobile-First Progressive:

<div className="text-sm sm:text-base lg:text-lg">

Semantic Token Usage:

<div className="bg-background text-foreground p-4 rounded-lg">

Design System Alignment:

<div className="space-y-4 p-lg">  {/* 8px grid spacing */}

Quick Reference - Common Patterns

Layout

Flexbox:

// Row with centered items
<div className="flex items-center gap-4">

// Column layout
<div className="flex flex-col items-start gap-2">

// Center content
<div className="flex items-center justify-center min-h-screen">

// Space between
<div className="flex items-center justify-between">

// Responsive wrap
<div className="flex flex-wrap gap-4">

Grid:

// Responsive columns
<div className="grid grid-cols-2 gap-4 md:grid-cols-3 lg:grid-cols-4">

// Sidebar layout
<div className="grid grid-cols-1 gap-6 lg:grid-cols-[2fr_1fr]">

// Equal height
<div className="grid auto-rows-fr gap-4">

Spacing (8px Grid)

// Micro spacing
<div className="gap-0.5">        {/* 2px */}
<div className="gap-1">          {/* 4px */}

// Standard grid (8px base)
<div className="gap-2">          {/* 8px */}
<div className="gap-3">          {/* 12px */}
<div className="gap-4">          {/* 16px */}
<div className="gap-6">          {/* 24px */}
<div className="gap-8">          {/* 32px */}

// Layout sections
<div className="gap-12">         {/* 48px */}
<div className="gap-16">         {/* 64px */}

Typography

// Headings (responsive)
<h1 className="text-2xl font-bold tracking-tight sm:text-3xl">
<h2 className="text-xl font-semibold">
<h3 className="text-lg font-medium">

// Body text
<p className="text-sm sm:text-base text-muted-foreground">

// Labels
<label className="text-sm font-medium">

Colors

// Semantic tokens
<div className="bg-background text-foreground">
<div className="bg-card text-card-foreground">
<div className="bg-primary text-primary-foreground">
<div className="bg-muted text-muted-foreground">

// Opacity modifiers
<div className="bg-primary/50 text-foreground/80">

// Hover states
<button className="hover:bg-primary/90">

Borders & Radius

// Borders
<div className="border border-border">
<div className="border-t border-b">

// Radius (pixel-perfect)
<div className="rounded-sm">    {/* 2px - badges */}
<div className="rounded-md">    {/* 6px - buttons/inputs */}
<div className="rounded-lg">    {/* 8px - cards (default) */}
<div className="rounded-xl">    {/* 12px - major elements */}
<div className="rounded-2xl">   {/* 16px - modals */}

Responsive Design

Breakpoints

// Mobile first progression
<div className="text-sm sm:text-base md:text-lg lg:text-xl">

// Show/hide at breakpoints
<div className="hidden lg:block">     {/* Desktop only */}
<div className="block lg:hidden">     {/* Mobile only */}

// Responsive grid
<div className="grid grid-cols-1 md:grid-cols-2 lg:grid-cols-3">

Breakpoint values:

• sm: 640px
• md: 768px
• lg: 1024px
• xl: 1280px
• 2xl: 1536px

Touch Targets (Mobile)

Minimum 44px for accessibility:

<Button size="default">    {/* h-11 mobile (44px), h-9 desktop */}
<Button size="icon">       {/* size-11 (44px minimum) */}

V4 Specific Features

CSS-First Configuration

Import Tailwind:

/* global.css */
@import "tailwindcss";

Define Theme:

@theme {
  --color-primary: #3b82f6;
  --color-secondary: #8b5cf6;
  --font-sans: Inter, system-ui, sans-serif;
  --spacing-custom: 18rem;
}

Custom Utilities:

@utility container-padding {
  padding-inline: 2rem;

  @media (min-width: 768px) {
    padding-inline: 4rem;
  }
}

Migration from V3

Directives change:

/* Old (v3) */
@tailwind base;
@tailwind components;
@tailwind utilities;

/* New (v4) */
@import "tailwindcss";

Theme moves to CSS:

// Old (v3) - tailwind.config.js
module.exports = {
  theme: {
    extend: {
      colors: { primary: '#3b82f6' }
    }
  }
}

// New (v4) - global.css
@theme {
  --color-primary: #3b82f6;
}

Accessibility

Focus States

// Standard focus ring
<button className="focus-visible:ring-2 focus-visible:ring-ring">

// Atlas reusable classes
<button className="focus-ring">
<button className="focus-ring-primary">

Color Contrast

// High contrast (WCAG AA)
<div className="bg-background text-foreground">

// Medium contrast (readable)
<p className="text-muted-foreground">

Screen Readers

// Hidden from visual, available to screen readers
<span className="sr-only">Hidden label</span>

// Icon buttons need labels
<Button size="icon" aria-label="Delete item">
  <Trash className="h-4 w-4" />
</Button>

// Skip links
<a className="skip-link" href="#main">Skip to content</a>

Common Component Patterns

Cards

<Card>
  <CardHeader>
    <CardTitle>Title</CardTitle>
  </CardHeader>
  <CardContent className="space-y-4">Content</CardContent>
</Card>

Forms

<form className="space-y-4">
  <div className="grid grid-cols-1 sm:grid-cols-2 gap-4">
    <FormField label="First Name">
      <Input />
    </FormField>
    <FormField label="Last Name">
      <Input />
    </FormField>
  </div>

  <div className="flex justify-end gap-2">
    <Button variant="outline">Cancel</Button>
    <Button type="submit">Save</Button>
  </div>
</form>

Buttons

// Variants
<Button variant="default">Primary</Button>
<Button variant="secondary">Secondary</Button>
<Button variant="outline">Outline</Button>
<Button variant="destructive">Delete</Button>

// Sizes
<Button size="sm">Small</Button>
<Button size="default">Default</Button>
<Button size="lg">Large</Button>

// Icon button (needs aria-label)
<Button size="icon" aria-label="Settings">
  <Settings className="h-4 w-4" />
</Button>

Dark Mode

Configuration

/* global.css */
@custom-variant dark (&:is(.dark *));

:root {
  --background: #ffffff;
  --foreground: #000000;
}

.dark {
  --background: #000000;
  --foreground: #ffffff;
}

Usage

// Automatic dark mode
<div className="bg-background text-foreground">

// Explicit override
<div className="bg-white dark:bg-gray-900">

Common Mistakes

Using v3 syntax:

/* Wrong */
@tailwind base;

/* Right */
@import "tailwindcss";

Off-grid spacing:

{/* Wrong - 4px off-grid */}
<div className="gap-1">

{/* Right - 8px on-grid */}
<div className="gap-2">

Missing focus states:

{/* Wrong */}
<button className="p-4">

{/* Right */}
<button className="p-4 focus-visible:ring-2">

Icon buttons without labels:

{
  /* Wrong - inaccessible */
}
<Button size="icon">
  <Trash />
</Button>;

{
  /* Right - accessible */
}
<Button size="icon" aria-label="Delete">
  <Trash />
</Button>;

Not mobile-first:

{/* Wrong - desktop-first */}
<div className="lg:text-lg text-sm">

{/* Right - mobile-first */}
<div className="text-sm lg:text-lg">

Resources

Reference Files

• references/patterns.md - Detailed implementation patterns
• references/recipes.md - Common use case solutions
• references/examples.md - Complete working examples

Atlas Documentation

• src/styles/global.css - Main stylesheet with @theme definitions
• framework/patterns/styling.md - Styling patterns
• framework/patterns/shadcn.md - Component integration
• src/components/ui/button.tsx - Button variants example

External Resources

• Tailwind v4 docs: https://tailwindcss.com/docs
• CSS-first config: https://tailwindcss.com/docs/v4-beta
• Migration guide: https://tailwindcss.com/docs/upgrade-guide

Next Steps

1. Review patterns: Read references/patterns.md for detailed implementations
2. Study recipes: Check references/recipes.md for specific use cases
3. See examples: Review references/examples.md for complete implementations
4. Practice: Build components using these patterns
5. Validate: Run pnpm lint to ensure code quality

Quick Implementation Guide

New component checklist:

1. Start with semantic layout (flex/grid)
2. Apply 8px grid spacing
3. Use semantic color tokens
4. Add responsive breakpoints
5. Include focus states
6. Test keyboard navigation
7. Verify color contrast
8. Add dark mode support