UI Design System

When to Use

Activate this skill when:

• Creating new UI components that must follow a design system
• Building page layouts with consistent spacing and structure
• Setting up or extending design tokens (colors, typography, spacing)
• Choosing colors, fonts, or spacing values for a project
• Reviewing UI code for design consistency and accessibility
• Integrating shadcn/ui components into existing layouts

Do NOT use this skill for:

• Backend API implementation (use python-backend-expert)
• Component or hook testing (use react-testing-patterns)
• E2E browser testing (use e2e-testing)
• General React patterns unrelated to design system (use react-frontend-expert)
• Deployment or CI/CD (use deployment-pipeline)

Instructions

Step 0: Read Existing Design Tokens

Before generating any UI code, check the project for existing tokens:

1. Read tailwind.config.ts (or .js) for custom theme extensions
2. Read src/styles/globals.css or app/globals.css for CSS custom properties
3. Read components.json if shadcn/ui is configured

If no design tokens exist, generate a starter set and ask the user to confirm before proceeding (see Edge Cases).

Design Tokens

Color Tokens

Define colors as CSS custom properties consumed by Tailwind. Never use hardcoded hex/rgb values in components.

CSS custom properties (HSL format for shadcn/ui compatibility):

/* globals.css */
@layer base {
  :root {
    --background: 0 0% 100%;
    --foreground: 222 47% 11%;
    --primary: 221 83% 53%;
    --primary-foreground: 210 40% 98%;
    --secondary: 210 40% 96%;
    --secondary-foreground: 222 47% 11%;
    --muted: 210 40% 96%;
    --muted-foreground: 215 16% 47%;
    --accent: 210 40% 96%;
    --accent-foreground: 222 47% 11%;
    --destructive: 0 84% 60%;
    --destructive-foreground: 210 40% 98%;
    --border: 214 32% 91%;
    --input: 214 32% 91%;
    --ring: 221 83% 53%;
    --radius: 0.5rem;
  }

  .dark {
    --background: 222 47% 11%;
    --foreground: 210 40% 98%;
    --primary: 217 91% 60%;
    --primary-foreground: 222 47% 11%;
    --secondary: 217 33% 17%;
    --secondary-foreground: 210 40% 98%;
    --muted: 217 33% 17%;
    --muted-foreground: 215 20% 65%;
    --accent: 217 33% 17%;
    --accent-foreground: 210 40% 98%;
    --destructive: 0 63% 31%;
    --destructive-foreground: 210 40% 98%;
    --border: 217 33% 17%;
    --input: 217 33% 17%;
    --ring: 224 76% 48%;
  }
}

Tailwind config mapping:

// tailwind.config.ts
export default {
  theme: {
    extend: {
      colors: {
        background: "hsl(var(--background))",
        foreground: "hsl(var(--foreground))",
        primary: {
          DEFAULT: "hsl(var(--primary))",
          foreground: "hsl(var(--primary-foreground))",
        },
        secondary: {
          DEFAULT: "hsl(var(--secondary))",
          foreground: "hsl(var(--secondary-foreground))",
        },
        muted: {
          DEFAULT: "hsl(var(--muted))",
          foreground: "hsl(var(--muted-foreground))",
        },
        accent: {
          DEFAULT: "hsl(var(--accent))",
          foreground: "hsl(var(--accent-foreground))",
        },
        destructive: {
          DEFAULT: "hsl(var(--destructive))",
          foreground: "hsl(var(--destructive-foreground))",
        },
        border: "hsl(var(--border))",
        input: "hsl(var(--input))",
        ring: "hsl(var(--ring))",
      },
    },
  },
} satisfies Config;

Color usage rules:

• Always use semantic token classes: bg-primary, text-foreground, border-border
• Never use raw Tailwind palette colors (bg-blue-500) in component code
• Every color must have a dark mode variant defined
• Use foreground variants for text on colored backgrounds

Typography Scale

Define a typographic scale using Tailwind's font-size utilities:

Typography rules:

• Set a base font in tailwind.config.ts: fontFamily: { sans: ["Inter", "system-ui", "sans-serif"] }
• Use font-medium (500) for headings and labels, font-normal (400) for body
• Use tracking-tight for headings text-2xl and above
• Limit line length with max-w-prose (65ch) for readability

Spacing (8pt Grid)

All spacing values follow an 8pt base grid:

Spacing rules:

• Use gap-* for flex/grid children instead of individual margins
• Prefer space-y-* for vertical stacking of sibling elements
• Cards: p-6 padding with gap-4 between internal elements
• Page sections: py-12 or py-16 vertical padding
• Never mix spacing systems (no margin: 13px)

Component Structure

Hierarchy: Container > Layout > Content

Every component follows a three-layer structure:

// Container: outer wrapper with spacing, background, border
<Card className="p-6">
  {/* Layout: flex/grid arrangement */}
  <div className="flex items-center gap-4">
    {/* Content: actual UI elements */}
    <Avatar src={user.avatar} alt={user.name} />
    <div className="space-y-1">
      <h3 className="text-sm font-medium">{user.name}</h3>
      <p className="text-sm text-muted-foreground">{user.role}</p>
    </div>
  </div>
</Card>

Semantic HTML

Use the correct HTML element for every purpose:

shadcn/ui Primitives

Prefer shadcn/ui components over custom implementations:

If shadcn/ui is not installed, fall back to plain Tailwind with equivalent patterns and consistent class ordering.

TypeScript Component Interfaces

Export props as TypeScript interfaces with JSDoc descriptions:

/** Props for the UserProfileCard component. */
interface UserProfileCardProps {
  /** User data to display. */
  user: User;
  /** Called when the edit button is clicked. */
  onEdit?: (userId: string) => void;
  /** Visual variant of the card. */
  variant?: "default" | "compact";
  /** Additional CSS classes applied to the root element. */
  className?: string;
}

export function UserProfileCard({
  user,
  onEdit,
  variant = "default",
  className,
}: UserProfileCardProps) {
  // ...
}

Props rules:

• Name interface {ComponentName}Props
• Include className?: string on every component for composition
• Use variant prop for visual variations, not separate components
• Default optional props in destructuring, not in interface
• Use union types for constrained string values: "sm" | "md" | "lg"

Responsive Design

Breakpoints

Use Tailwind's mobile-first breakpoints:

Responsive rules:

• Design mobile-first: base styles for mobile, then add breakpoint overrides
• Use grid-cols-1 md:grid-cols-2 lg:grid-cols-3 for responsive grids
• Stack navigation vertically on mobile: flex-col md:flex-row
• Hide non-essential elements on mobile: hidden md:block
• Set max container width: max-w-7xl mx-auto px-4 sm:px-6 lg:px-8

Responsive Layout Pattern

<div className="max-w-7xl mx-auto px-4 sm:px-6 lg:px-8">
  <div className="grid grid-cols-1 md:grid-cols-2 lg:grid-cols-3 gap-6">
    {items.map((item) => (
      <ItemCard key={item.id} item={item} />
    ))}
  </div>
</div>

Accessibility (WCAG 2.1 AA)

Contrast Ratios

• Normal text (< 18px or < 14px bold): minimum 4.5:1 contrast ratio
• Large text (>= 18px or >= 14px bold): minimum 3:1 contrast ratio
• UI components and graphical objects: minimum 3:1 contrast ratio

Interactive Element Requirements

Every interactive element must have:

1. Visible label or aria-label: <Button aria-label="Close dialog">X</Button>
2. Focus indicator: Tailwind's ring utilities: focus-visible:ring-2 focus-visible:ring-ring
3. Keyboard access: Reachable via Tab, activatable via Enter/Space
4. Disabled state: Both visual and aria-disabled or disabled attribute

ARIA Patterns

• Icon-only buttons: aria-label="Delete item"
• Loading states: aria-busy="true" on the loading container
• Dynamic content updates: aria-live="polite" on the container
• Form errors: aria-invalid="true" on the input, role="alert" on the message
• Modals: aria-modal="true", focus trap, Escape to close
• Navigation landmarks: <nav aria-label="Main navigation">

Examples

User Profile Card

interface UserProfileCardProps {
  user: { id: string; name: string; role: string; avatarUrl: string };
  onEdit?: (userId: string) => void;
  className?: string;
}

export function UserProfileCard({ user, onEdit, className }: UserProfileCardProps) {
  return (
    <Card className={cn("p-6", className)}>
      <div className="flex items-center gap-4">
        <Avatar className="h-12 w-12">
          <AvatarImage src={user.avatarUrl} alt={user.name} />
          <AvatarFallback>{user.name.charAt(0)}</AvatarFallback>
        </Avatar>
        <div className="space-y-1">
          <h3 className="text-sm font-medium leading-none">{user.name}</h3>
          <p className="text-sm text-muted-foreground">{user.role}</p>
        </div>
      </div>
      {onEdit && (
        <div className="mt-4">
          <Button
            variant="outline"
            size="sm"
            onClick={() => onEdit(user.id)}
            aria-label={`Edit ${user.name}'s profile`}
          >
            Edit Profile
          </Button>
        </div>
      )}
    </Card>
  );
}

SaaS Dashboard Design Tokens Setup

Tailwind config extension:

// tailwind.config.ts
import type { Config } from "tailwindcss";

export default {
  theme: {
    extend: {
      colors: {
        background: "hsl(var(--background))",
        foreground: "hsl(var(--foreground))",
        primary: {
          DEFAULT: "hsl(var(--primary))",
          foreground: "hsl(var(--primary-foreground))",
        },
        secondary: {
          DEFAULT: "hsl(var(--secondary))",
          foreground: "hsl(var(--secondary-foreground))",
        },
        muted: {
          DEFAULT: "hsl(var(--muted))",
          foreground: "hsl(var(--muted-foreground))",
        },
        accent: {
          DEFAULT: "hsl(var(--accent))",
          foreground: "hsl(var(--accent-foreground))",
        },
        destructive: {
          DEFAULT: "hsl(var(--destructive))",
          foreground: "hsl(var(--destructive-foreground))",
        },
        border: "hsl(var(--border))",
        input: "hsl(var(--input))",
        ring: "hsl(var(--ring))",
      },
      fontFamily: {
        sans: ["Inter", "system-ui", "sans-serif"],
      },
      borderRadius: {
        lg: "var(--radius)",
        md: "calc(var(--radius) - 2px)",
        sm: "calc(var(--radius) - 4px)",
      },
    },
  },
} satisfies Config;

Responsive Dashboard Layout

export function DashboardLayout({ children }: { children: React.ReactNode }) {
  return (
    <div className="min-h-screen bg-background">
      <nav className="border-b border-border" aria-label="Main navigation">
        <div className="max-w-7xl mx-auto px-4 sm:px-6 lg:px-8 h-16 flex items-center">
          {/* nav content */}
        </div>
      </nav>
      <div className="max-w-7xl mx-auto px-4 sm:px-6 lg:px-8 py-8">
        <div className="grid grid-cols-1 lg:grid-cols-[240px_1fr] gap-8">
          <aside className="hidden lg:block" aria-label="Sidebar">
            {/* sidebar content */}
          </aside>
          <main>{children}</main>
        </div>
      </div>
    </div>
  );
}

Edge Cases

• No existing design tokens: Generate a starter token set (see references/design-tokens-reference.md) and present it to the user for confirmation before writing any component code. Ask: "No design tokens found. Here's a starter set — should I apply these?"

• shadcn/ui not installed: Fall back to plain Tailwind with equivalent patterns. Use <button className="..."> instead of <Button>, styled <div> instead of <Card>. Maintain the same spacing and color token approach.

• Component overlap: If a requested component duplicates an existing one, flag it: "A similar UserCard component exists at src/components/UserCard.tsx. Should I extend it or create a separate component?"

• Dark mode tokens missing: If :root tokens exist but .dark variants are absent, generate matching dark variants before proceeding. Every semantic color token must have both light and dark values.

• Custom brand colors: When the user provides specific brand hex values, convert them to HSL and integrate into the token system. Never use the hex values directly in components.

• Inconsistent spacing in existing code: Flag the inconsistency, suggest the closest 8pt grid values, and ask whether to normalize existing components or only apply the grid to new code.

See references/design-tokens-reference.md for starter token sets, color palette guide, and typography scales.