Agent skill

shadcn-ui-patterns

shadcn/ui component patterns for this project. CVA variants, data-slot pattern, Radix composition, mobile touch targets. Triggers on "shadcn", "ui component", "cva", "class-variance-authority", "data-slot".

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SKILL.md

shadcn/ui Patterns

New York style variant with Tailwind v4. All components in src/components/ui/. Uses class-variance-authority for type-safe variants, Radix UI for primitives.

Component Structure

Two types: variant-based (Button, Badge) and composition-based (Card).

Variant-Based (cva)

typescript
// From components/ui/button.tsx
import { Slot } from "@radix-ui/react-slot";
import { cva, type VariantProps } from "class-variance-authority";
import { cn } from "@/lib/utils";

const buttonVariants = cva(
  "inline-flex items-center justify-center gap-2 whitespace-nowrap rounded-md text-sm font-medium transition-all duration-200 ease-out disabled:pointer-events-none disabled:opacity-50 [&_svg]:pointer-events-none [&_svg:not([class*='size-'])]:size-4 shrink-0",
  {
    variants: {
      variant: {
        default: "bg-primary text-primary-foreground hover:bg-primary/90",
        destructive: "bg-destructive text-white hover:bg-destructive/90",
        outline: "border bg-background shadow-xs hover:bg-accent",
        ghost: "hover:bg-accent hover:text-accent-foreground",
        link: "text-primary underline-offset-4 hover:underline",
      },
      size: {
        default: "h-9 px-4 py-2 has-[>svg]:px-3 min-h-[44px] sm:min-h-0",
        sm: "h-8 rounded-md gap-1.5 px-3 min-h-[44px] sm:min-h-0",
        lg: "h-10 rounded-md px-6 min-h-[44px] sm:min-h-0",
        icon: "size-9 min-h-[44px] min-w-[44px] sm:size-9",
      },
    },
    defaultVariants: {
      variant: "default",
      size: "default",
    },
  },
);

function Button({
  className,
  variant,
  size,
  asChild = false,
  ...props
}: React.ComponentProps<"button"> &
  VariantProps<typeof buttonVariants> & {
    asChild?: boolean;
  }) {
  const Comp = asChild ? Slot : "button";

  return (
    <Comp
      data-slot="button"
      className={cn(buttonVariants({ variant, size, className }))}
      {...props}
    />
  );
}

export { Button, buttonVariants };

Composition-Based (no cva)

typescript
// From components/ui/card.tsx
function Card({ className, ...props }: React.ComponentProps<"div">) {
  return (
    <div
      data-slot="card"
      className={cn(
        "bg-card text-card-foreground flex flex-col gap-6 rounded-xl border py-6 shadow-sm",
        className,
      )}
      {...props}
    />
  );
}

function CardHeader({ className, ...props }: React.ComponentProps<"div">) {
  return (
    <div
      data-slot="card-header"
      className={cn(
        "@container/card-header grid auto-rows-min grid-rows-[auto_auto] items-start gap-2 px-6 has-data-[slot=card-action]:grid-cols-[1fr_auto]",
        className,
      )}
      {...props}
    />
  );
}

function CardTitle({ className, ...props }: React.ComponentProps<"div">) {
  return (
    <div
      data-slot="card-title"
      className={cn("leading-none font-semibold", className)}
      {...props}
    />
  );
}

export { Card, CardHeader, CardTitle, CardDescription, CardContent, CardFooter, CardAction };

Variant Pattern

Standard structure:

  1. Base classes (always applied)
  2. variants object with categories (variant, size, etc.)
  3. defaultVariants for sensible defaults
  4. Export both component and variants (for external use)
typescript
// From components/ui/badge.tsx
const badgeVariants = cva(
  "inline-flex items-center justify-center rounded-full border px-2 py-0.5 text-xs font-medium w-fit whitespace-nowrap",
  {
    variants: {
      variant: {
        default: "border-transparent bg-primary text-primary-foreground",
        secondary: "border-transparent bg-secondary text-secondary-foreground",
        destructive: "border-transparent bg-destructive text-white",
        outline: "text-foreground [a&]:hover:bg-accent",
      },
    },
    defaultVariants: {
      variant: "default",
    },
  },
);

asChild Pattern (Radix Slot)

Allow polymorphic rendering - render as different element while keeping styles.

typescript
// Usage
<Button asChild>
  <Link href="/dashboard">Go to Dashboard</Link>
</Button>

// Renders as: <a href="/dashboard" class="button-classes">Go to Dashboard</a>

Implementation:

typescript
import { Slot } from "@radix-ui/react-slot";

function Button({ asChild = false, ...props }) {
  const Comp = asChild ? Slot : "button";
  return <Comp {...props} />;
}

Use for: Button, Badge. Don't use for: simple divs (Card, Input).

cn() Utility

Merges Tailwind classes intelligently - resolves conflicts (last one wins).

typescript
// From lib/utils.ts
import { type ClassValue, clsx } from "clsx";
import { twMerge } from "tailwind-merge";

export function cn(...inputs: ClassValue[]) {
  return twMerge(clsx(inputs));
}

// Usage
<Input className={cn("h-12", className)} />
// If user passes "h-8", result is "h-8" (not "h-12 h-8")

Always use in components: className={cn(baseClasses, className)}

data-slot Pattern

All components use data-slot attribute for targeted styling by parent selectors.

typescript
// From components/ui/input.tsx
<input
  data-slot="input"
  className={cn("...", className)}
/>

// From components/ui/card.tsx
<div data-slot="card-header" className={cn(
  "@container/card-header grid ... has-data-[slot=card-action]:grid-cols-[1fr_auto]",
  className
)} />

CardHeader uses it: detects CardAction presence with has-data-[slot=card-action], adjusts grid layout.

Use for:

  • Parent-child component communication (Card detecting CardAction)
  • Scoped styles in multi-component patterns
  • Debug/testing selectors

Mobile Touch Targets (44px)

CRITICAL: All interactive elements must be 44x44px minimum on mobile (iOS/Android HIG).

typescript
// From components/ui/button.tsx
size: {
  default: "h-9 px-4 py-2 min-h-[44px] sm:min-h-0",  // 44px mobile, 36px desktop
  icon: "size-9 min-h-[44px] min-w-[44px] sm:size-9", // 44x44 mobile, 36x36 desktop
}

Pattern: min-h-[44px] sm:min-h-0 for height, min-h-[44px] min-w-[44px] sm:size-X for icons.

Apply to: Button, Badge (when interactive), Toggle, Switch, Checkbox, Radio, any clickable element.

Focus States

Consistent focus ring across all interactive components.

typescript
// Standard pattern
className={cn(
  "outline-none",
  "focus-visible:border-ring focus-visible:ring-ring/50 focus-visible:ring-[3px]",
  "aria-invalid:ring-destructive/20 dark:aria-invalid:ring-destructive/40 aria-invalid:border-destructive",
  className
)}
  • focus-visible: only on keyboard navigation (not mouse click)
  • 3px ring width with 50% opacity
  • Invalid state: destructive ring color

From: components/ui/input.tsx, button.tsx

SVG Icon Handling

Auto-size and style icons inside components.

typescript
// From components/ui/button.tsx
"[&_svg]:pointer-events-none [&_svg:not([class*='size-'])]:size-4 shrink-0 [&_svg]:shrink-0"

// Usage
<Button>
  <Upload /> {/* Auto-sized to size-4 (16px) */}
  Upload File
</Button>

Pattern: [&_svg]:size-4 (16px default), [&_svg]:pointer-events-none (clicks go to button), shrink-0 (prevent squish).

Badge uses [&>svg]:size-3 (12px for smaller badges).

Installation

bash
bunx shadcn@latest add button
bunx shadcn@latest add card

Config: components.json at repo root.

json
{
  "style": "new-york",
  "rsc": true,
  "aliases": {
    "components": "@/components",
    "utils": "@/lib/utils",
    "ui": "@/components/ui"
  }
}

Customization

Edit directly in components/ui/ - they're source files, not library code.

Common customizations:

  • Change variant colors: edit cva variants
  • Add new sizes: add to variants object
  • Adjust animations: edit base classes or add new compound variants
  • Mobile breakpoints: change sm: prefix in min-h overrides

Don't:

  • Wrap in another component just to change styles - edit the source
  • Create custom variants externally - add to cva definition

Composition Patterns

Card with action button:

typescript
<Card>
  <CardHeader>
    <CardTitle>Title</CardTitle>
    <CardDescription>Description</CardDescription>
    <CardAction>
      <Button variant="ghost" size="icon">
        <MoreHorizontal />
      </Button>
    </CardAction>
  </CardHeader>
  <CardContent>Content here</CardContent>
</Card>

CardHeader detects CardAction via has-data-[slot=card-action], switches to 2-column grid.

Key Files

  • src/components/ui/button.tsx - Variant-based with asChild, mobile touch, icon handling
  • src/components/ui/badge.tsx - Variant-based with asChild, link hover states
  • src/components/ui/card.tsx - Composition-based, grid layout detection
  • src/components/ui/input.tsx - Simple wrapper, focus/invalid states
  • src/lib/utils.ts - cn() utility
  • components.json - shadcn config (New York style, RSC, aliases)

Avoid

  • Don't use clsx alone - always use cn() (merges Tailwind conflicts)
  • Don't skip data-slot - used by parent components for layout detection
  • Don't forget mobile touch targets - add min-h-[44px] sm:min-h-0 to interactive elements
  • Don't create wrapper components - edit source files in components/ui/ directly
  • Don't mix variant approaches - use cva for multiple variants, plain cn() for simple components
  • Don't hardcode Radix component names - use asChild pattern for polymorphism

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