Skill: shadcn

Scope

• Applies to: Tailwind v4 with shadcn/ui setup, CSS variable architecture, dark mode, theme configuration, component composition patterns, accessibility, form integration
• Does NOT cover: Tailwind v3, PostCSS configuration

Assumptions

• Tailwind CSS v4+
• shadcn/ui latest
• Next.js 16 (this repo); CSS-first Tailwind v4, not Vite
• React 18+ or Next.js 14+
• TypeScript 6+

Principles

• Use @theme inline to map CSS variables to Tailwind tokens
• Use hsl() wrapper for color values in :root and .dark
• Set "tailwind.config": "" in components.json (empty for v4)
• Delete tailwind.config.ts if it exists (v4 uses CSS-based config)
• Use CSS-first Tailwind v4 in the Next app (not @tailwindcss/vite)
• Use cn() utility for conditional classes
• Semantic colors automatically adapt to dark mode (no dark: variants needed)
• Use @plugin directive for plugins (not @import or require())
• Compose complex components from smaller shadcn primitives
• Extend components via wrapper pattern (don't modify originals)
• Use CVA (class-variance-authority) for variant systems
• Use forwardRef only when a parent must attach a ref (React 19 does not require it by default)
• Leverage Radix UI primitives for built-in accessibility

Constraints

MUST

• Wrap color values with hsl() in :root and .dark
• Use @theme inline to map all CSS variables
• Set "tailwind.config": "" in components.json
• Delete tailwind.config.ts if it exists
• Use CSS-first Tailwind v4 in Next apps (@import "tailwindcss" in CSS)

SHOULD

• Use semantic color tokens (--background, --foreground, etc.)
• Use cn() utility for conditional classes
• Use @plugin directive for plugins
• Compose components from smaller shadcn primitives
• Use wrapper pattern to extend components (don't modify originals)
• Use CVA for variant systems in custom components
• Use forwardRef when a parent must attach a ref
• Test accessibility with keyboard navigation and screen readers
• Use Radix UI primitives for complex interactions (dialogs, dropdowns, etc.)
• Provide ARIA labels for icon-only buttons and interactive elements
• Use @tailwindcss/vite only when the app is Vite-based (not Next.js)

AVOID

• Putting :root or .dark inside @layer base
• Using .dark { @theme { } } pattern (v4 doesn't support nested @theme)
• Double-wrapping colors (hsl(var(--background)) in body)
• Using tailwind.config.ts for theme colors
• Using @apply directive (deprecated in v4)
• Using dark: variants for semantic colors
• Using @import or require() for plugins (use @plugin)
• Modifying base shadcn components directly (use wrapper pattern)
• Building custom dropdowns/dialogs from scratch (use Radix primitives)
• Relying on color alone for state indication
• Skipping accessibility testing

Interactions

• Works with next for App Router setup
• Uses typescript for type safety

Patterns

CSS Variable Setup

/* src/index.css */
@import "tailwindcss";

@theme inline {
  --color-background: var(--background);
  --color-foreground: var(--foreground);
}

:root {
  --background: hsl(0 0% 100%);
  --foreground: hsl(222.2 84% 4.9%);
}

.dark {
  --background: hsl(222.2 84% 4.9%);
  --foreground: hsl(210 40% 98%);
}

Vite Configuration (Vite apps only)

// vite.config.ts — skip for Next.js CSS-first setups
import tailwindcss from '@tailwindcss/vite'

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

Components Config

{
  "tailwind": {
    "config": "",
    "css": "src/index.css",
    "baseColor": "slate",
    "cssVariables": true
  }
}

See Templates (including Component Extension) and Architecture for complete setup.

References

• Architecture - Complete setup pattern
• Dark Mode - Dark mode implementation
• Common Gotchas - Common issues and fixes
• Migration Guide - Migrating from v3
• Component Patterns - Composition, CVA, extension patterns
• Accessibility - ARIA, keyboard navigation, screen readers
• Form Patterns - React Hook Form integration

Resources

• shadcn/ui Tailwind v4 Guide
• Tailwind v4 Docs