# UI/UX Design Expert Skill

## Activation Criteria
Activate this skill when the user:
- Requests creation of design systems or component libraries
- Asks for responsive layouts, mobile-first design, or cross-device interfaces
- Needs color schemes, typography pairing, or visual identity systems
- Requires accessibility compliance (WCAG 2.1, ARIA labels)
- Wants CSS/Tailwind implementations for UI components
- Requests Figma-to-code conversions or design token systems
- Needs dark mode implementation or theme switching
- Asks for animation, micro-interactions, or motion design
- Requires specific UI styles: glassmorphism, neumorphism, minimalism, brutalism
- Is building: web apps, dashboards, e-commerce sites, SaaS platforms, admin panels
- Needs CSS Grid, Flexbox, or modern layout mastery

## Core Methodology

### 1. Design System Foundation

#### Step 1: Define Design Tokens
Start with atomic design tokens that form the foundation of all visual decisions.

```css
/* Design Tokens - CSS Custom Properties */
:root {
  /* Color Palette - Primary */
  --color-primary-50: #eff6ff;
  --color-primary-100: #dbeafe;
  --color-primary-200: #bfdbfe;
  --color-primary-300: #93c5fd;
  --color-primary-400: #60a5fa;
  --color-primary-500: #3b82f6;
  --color-primary-600: #2563eb;
  --color-primary-700: #1d4ed8;
  --color-primary-800: #1e40af;
  --color-primary-900: #1e3a8a;

  /* Semantic Colors */
  --color-success: #10b981;
  --color-warning: #f59e0b;
  --color-error: #ef4444;
  --color-info: #3b82f6;

  /* Neutral Scale */
  --color-gray-50: #f9fafb;
  --color-gray-100: #f3f4f6;
  --color-gray-200: #e5e7eb;
  --color-gray-300: #d1d5db;
  --color-gray-400: #9ca3af;
  --color-gray-500: #6b7280;
  --color-gray-600: #4b5563;
  --color-gray-700: #374151;
  --color-gray-800: #1f2937;
  --color-gray-900: #111827;

  /* Typography Scale */
  --font-family-base: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --font-family-mono: 'SF Mono', Monaco, 'Cascadia Code', monospace;

  /* Font Sizes - Type Scale (Major Third) */
  --text-xs: 0.75rem;     /* 12px */
  --text-sm: 0.875rem;    /* 14px */
  --text-base: 1rem;      /* 16px */
  --text-lg: 1.125rem;    /* 18px */
  --text-xl: 1.25rem;     /* 20px */
  --text-2xl: 1.5rem;     /* 24px */
  --text-3xl: 1.875rem;   /* 30px */
  --text-4xl: 2.25rem;    /* 36px */
  --text-5xl: 3rem;       /* 48px */

  /* Spacing Scale (4px base unit) */
  --spacing-1: 0.25rem;   /* 4px */
  --spacing-2: 0.5rem;    /* 8px */
  --spacing-3: 0.75rem;   /* 12px */
  --spacing-4: 1rem;      /* 16px */
  --spacing-5: 1.25rem;   /* 20px */
  --spacing-6: 1.5rem;    /* 24px */
  --spacing-8: 2rem;      /* 32px */
  --spacing-10: 2.5rem;   /* 40px */
  --spacing-12: 3rem;     /* 48px */
  --spacing-16: 4rem;     /* 64px */
  --spacing-20: 5rem;     /* 80px */

  /* Border Radius */
  --radius-sm: 0.25rem;
  --radius-md: 0.375rem;
  --radius-lg: 0.5rem;
  --radius-xl: 0.75rem;
  --radius-2xl: 1rem;
  --radius-full: 9999px;

  /* Shadows */
  --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1);
  --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1);
  --shadow-xl: 0 20px 25px -5px rgb(0 0 0 / 0.1);

  /* Transitions */
  --transition-fast: 150ms ease-in-out;
  --transition-base: 200ms ease-in-out;
  --transition-slow: 300ms ease-in-out;

  /* Z-Index Scale */
  --z-base: 0;
  --z-dropdown: 1000;
  --z-sticky: 1020;
  --z-fixed: 1030;
  --z-modal-backdrop: 1040;
  --z-modal: 1050;
  --z-popover: 1060;
  --z-tooltip: 1070;
}
```

#### Tailwind Token Configuration

```javascript
// tailwind.config.js
module.exports = {
  theme: {
    extend: {
      colors: {
        primary: {
          50: '#eff6ff',
          100: '#dbeafe',
          200: '#bfdbfe',
          300: '#93c5fd',
          400: '#60a5fa',
          500: '#3b82f6',
          600: '#2563eb',
          700: '#1d4ed8',
          800: '#1e40af',
          900: '#1e3a8a',
        },
      },
      fontFamily: {
        sans: ['Inter', 'system-ui', 'sans-serif'],
        mono: ['Fira Code', 'monospace'],
      },
      spacing: {
        '18': '4.5rem',
        '88': '22rem',
        '128': '32rem',
      },
      animation: {
        'fade-in': 'fadeIn 0.2s ease-in-out',
        'slide-up': 'slideUp 0.3s ease-out',
        'slide-down': 'slideDown 0.3s ease-out',
        'scale-in': 'scaleIn 0.2s ease-out',
      },
      keyframes: {
        fadeIn: {
          '0%': { opacity: '0' },
          '100%': { opacity: '1' },
        },
        slideUp: {
          '0%': { transform: 'translateY(10px)', opacity: '0' },
          '100%': { transform: 'translateY(0)', opacity: '1' },
        },
        slideDown: {
          '0%': { transform: 'translateY(-10px)', opacity: '0' },
          '100%': { transform: 'translateY(0)', opacity: '1' },
        },
        scaleIn: {
          '0%': { transform: 'scale(0.95)', opacity: '0' },
          '100%': { transform: 'scale(1)', opacity: '1' },
        },
      },
    },
  },
  plugins: [
    require('@tailwindcss/forms'),
    require('@tailwindcss/typography'),
    require('@tailwindcss/aspect-ratio'),
  ],
};
```

### 2. Typography Systems

#### Font Pairing Strategy

**Principle: Contrast without Conflict**

```css
/* Professional Pairing 1: Modern SaaS */
:root {
  --font-heading: 'SF Pro Display', -apple-system, sans-serif;
  --font-body: 'Inter', system-ui, sans-serif;
  --font-mono: 'SF Mono', 'Fira Code', monospace;
}

/* Professional Pairing 2: Editorial */
:root {
  --font-heading: 'Merriweather', Georgia, serif;
  --font-body: 'Source Sans Pro', system-ui, sans-serif;
  --font-mono: 'IBM Plex Mono', monospace;
}

/* Professional Pairing 3: Tech/Developer */
:root {
  --font-heading: 'JetBrains Mono', monospace;
  --font-body: 'Geist', 'SF Pro', system-ui, sans-serif;
  --font-mono: 'Fira Code', monospace;
}
```

#### Typography Scale Implementation

```css
/* Type Scale with Responsive Adjustments */
.heading-1 {
  font-size: clamp(2.5rem, 5vw + 1rem, 4rem);
  font-weight: 700;
  line-height: 1.1;
  letter-spacing: -0.02em;
}

.heading-2 {
  font-size: clamp(2rem, 4vw + 0.5rem, 3rem);
  font-weight: 600;
  line-height: 1.2;
  letter-spacing: -0.01em;
}

.heading-3 {
  font-size: clamp(1.5rem, 2vw + 0.5rem, 2rem);
  font-weight: 600;
  line-height: 1.3;
}

.body-large {
  font-size: 1.125rem;
  line-height: 1.7;
}

.body-base {
  font-size: 1rem;
  line-height: 1.6;
}

.body-small {
  font-size: 0.875rem;
  line-height: 1.5;
}

.caption {
  font-size: 0.75rem;
  line-height: 1.4;
  color: var(--color-gray-500);
}
```

#### Tailwind Typography Implementation

```html
<!-- Using Tailwind's @apply for component patterns -->
<button class="btn-primary">
  Button Text
</button>

<style>
  @layer components {
    .btn-primary {
      @apply px-6 py-3 bg-primary-600 text-white font-semibold rounded-lg
             shadow-md hover:bg-primary-700 focus:outline-none focus:ring-2
             focus:ring-primary-500 focus:ring-offset-2
             transition-colors duration-150;
    }
  }
</style>
```

### 3. Color System Design

#### Color Theory Application

**Complementary Scheme for CTAs**
```css
/* High contrast for call-to-actions */
:root {
  --color-action-primary: #2563eb;  /* Blue */
  --color-action-secondary: #10b981; /* Green complement */
}
```

**Analogous Scheme for Navigation**
```css
/* Harmonious navigation colors */
:root {
  --color-nav-base: #3b82f6;
  --color-nav-hover: #60a5fa;
  --color-nav-active: #2563eb;
}
```

**Triadic Scheme for Status**
```css
/* Balanced status indicators */
:root {
  --color-success: #10b981;  /* Green */
  --color-warning: #f59e0b;  /* Orange */
  --color-error: #ef4444;    /* Red */
}
```

#### Dark Mode Implementation

```css
/* Dark mode color mapping */
@media (prefers-color-scheme: dark) {
  :root {
    --color-bg-primary: #111827;
    --color-bg-secondary: #1f2937;
    --color-bg-tertiary: #374151;
    --color-text-primary: #f9fafb;
    --color-text-secondary: #d1d5db;
    --color-text-tertiary: #9ca3af;
    --color-border: #374151;
  }
}

/* Manual dark mode toggle support */
[data-theme="dark"] {
  --color-bg-primary: #111827;
  --color-bg-secondary: #1f2937;
  --color-text-primary: #f9fafb;
  /* ... additional mappings */
}

[data-theme="light"] {
  --color-bg-primary: #ffffff;
  --color-bg-secondary: #f9fafb;
  --color-text-primary: #111827;
  /* ... additional mappings */
}
```

#### Tailwind Dark Mode Strategy

```javascript
// tailwind.config.js
module.exports = {
  darkMode: 'class', // or 'media'
  theme: {
    extend: {},
  },
};
```

```html
<!-- Implementation -->
<div class="bg-white dark:bg-gray-900 text-gray-900 dark:text-white">
  <h1 class="text-2xl dark:text-gray-100">Adaptive Heading</h1>
  <p class="text-gray-600 dark:text-gray-400">
    Responsive to theme changes
  </p>
</div>
```

### 4. Component Library Design

#### Button Component System

```css
/* Base Button */
.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--spacing-2);
  padding: var(--spacing-3) var(--spacing-6);
  font-size: var(--text-sm);
  font-weight: 500;
  line-height: 1;
  border-radius: var(--radius-md);
  border: 1px solid transparent;
  cursor: pointer;
  transition: all var(--transition-base);
}

/* Button Variants */
.button-primary {
  background-color: var(--color-primary-600);
  color: white;
  box-shadow: var(--shadow-sm);
}

.button-primary:hover {
  background-color: var(--color-primary-700);
  box-shadow: var(--shadow-md);
}

.button-primary:active {
  transform: translateY(1px);
}

.button-secondary {
  background-color: white;
  color: var(--color-gray-700);
  border-color: var(--color-gray-300);
}

.button-secondary:hover {
  background-color: var(--color-gray-50);
  border-color: var(--color-gray-400);
}

.button-ghost {
  background-color: transparent;
  color: var(--color-gray-700);
}

.button-ghost:hover {
  background-color: var(--color-gray-100);
}

/* Button Sizes */
.button-sm {
  padding: var(--spacing-2) var(--spacing-4);
  font-size: var(--text-xs);
}

.button-lg {
  padding: var(--spacing-4) var(--spacing-8);
  font-size: var(--text-base);
}

/* Button States */
.button:disabled {
  opacity: 0.5;
  cursor: not-allowed;
  pointer-events: none;
}

.button-loading {
  position: relative;
  color: transparent;
}

.button-loading::after {
  content: '';
  position: absolute;
  width: 1rem;
  height: 1rem;
  border: 2px solid currentColor;
  border-top-color: transparent;
  border-radius: 50%;
  animation: spin 0.6s linear infinite;
}

@keyframes spin {
  to { transform: rotate(360deg); }
}
```

#### Tailwind Button Component

```html
<!-- Primary Button -->
<button class="inline-flex items-center justify-center gap-2
               px-6 py-3 text-sm font-medium text-white
               bg-blue-600 rounded-lg shadow-sm
               hover:bg-blue-700 hover:shadow-md
               active:translate-y-px
               focus:outline-none focus:ring-2 focus:ring-blue-500 focus:ring-offset-2
               disabled:opacity-50 disabled:cursor-not-allowed
               transition-all duration-200">
  <svg class="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">
    <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M12 4v16m8-8H4"/>
  </svg>
  Create New
</button>

<!-- Secondary Button -->
<button class="inline-flex items-center justify-center gap-2
               px-6 py-3 text-sm font-medium text-gray-700
               bg-white border border-gray-300 rounded-lg
               hover:bg-gray-50 hover:border-gray-400
               active:translate-y-px
               focus:outline-none focus:ring-2 focus:ring-blue-500 focus:ring-offset-2
               transition-all duration-200">
  Cancel
</button>

<!-- Ghost Button -->
<button class="inline-flex items-center justify-center gap-2
               px-6 py-3 text-sm font-medium text-gray-700
               bg-transparent rounded-lg
               hover:bg-gray-100
               active:translate-y-px
               focus:outline-none focus:ring-2 focus:ring-blue-500 focus:ring-offset-2
               transition-all duration-200">
  Learn More
</button>
```

#### Form Component System

```css
/* Input Component */
.input {
  width: 100%;
  padding: var(--spacing-3) var(--spacing-4);
  font-size: var(--text-base);
  line-height: 1.5;
  color: var(--color-gray-900);
  background-color: white;
  border: 1px solid var(--color-gray-300);
  border-radius: var(--radius-md);
  transition: all var(--transition-base);
}

.input:hover {
  border-color: var(--color-gray-400);
}

.input:focus {
  outline: none;
  border-color: var(--color-primary-500);
  box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.1);
}

.input:disabled {
  background-color: var(--color-gray-100);
  color: var(--color-gray-500);
  cursor: not-allowed;
}

/* Error State */
.input-error {
  border-color: var(--color-error);
}

.input-error:focus {
  border-color: var(--color-error);
  box-shadow: 0 0 0 3px rgba(239, 68, 68, 0.1);
}

/* Input with Label */
.form-group {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-2);
}

.form-label {
  font-size: var(--text-sm);
  font-weight: 500;
  color: var(--color-gray-700);
}

.form-label-required::after {
  content: ' *';
  color: var(--color-error);
}

.form-hint {
  font-size: var(--text-xs);
  color: var(--color-gray-500);
}

.form-error {
  font-size: var(--text-xs);
  color: var(--color-error);
}
```

#### Tailwind Form Components

```html
<!-- Text Input -->
<div class="space-y-2">
  <label for="email" class="block text-sm font-medium text-gray-700">
    Email Address
  </label>
  <input
    type="email"
    id="email"
    class="block w-full px-4 py-3 text-base text-gray-900
           bg-white border border-gray-300 rounded-lg
           hover:border-gray-400
           focus:outline-none focus:ring-2 focus:ring-blue-500 focus:border-transparent
           disabled:bg-gray-100 disabled:text-gray-500 disabled:cursor-not-allowed
           transition-colors duration-200"
    placeholder="you@example.com"
  />
  <p class="text-xs text-gray-500">
    We'll never share your email with anyone else.
  </p>
</div>

<!-- Select Input -->
<div class="space-y-2">
  <label for="country" class="block text-sm font-medium text-gray-700">
    Country
  </label>
  <select
    id="country"
    class="block w-full px-4 py-3 text-base text-gray-900
           bg-white border border-gray-300 rounded-lg
           hover:border-gray-400
           focus:outline-none focus:ring-2 focus:ring-blue-500 focus:border-transparent
           transition-colors duration-200"
  >
    <option>United States</option>
    <option>Canada</option>
    <option>Mexico</option>
  </select>
</div>

<!-- Checkbox -->
<div class="flex items-start gap-3">
  <input
    type="checkbox"
    id="terms"
    class="mt-1 w-4 h-4 text-blue-600 border-gray-300 rounded
           focus:ring-2 focus:ring-blue-500"
  />
  <label for="terms" class="text-sm text-gray-700">
    I agree to the <a href="#" class="text-blue-600 hover:underline">Terms and Conditions</a>
  </label>
</div>
```

### 5. Layout Systems

#### CSS Grid Mastery

```css
/* Responsive Grid System */
.grid-container {
  display: grid;
  gap: var(--spacing-6);
}

/* Two Column Layout */
.grid-two {
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
}

/* Three Column Layout */
.grid-three {
  grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
}

/* Dashboard Grid */
.dashboard-grid {
  display: grid;
  grid-template-columns: 240px 1fr 300px;
  grid-template-rows: auto 1fr auto;
  grid-template-areas:
    "header header header"
    "sidebar main aside"
    "footer footer footer";
  min-height: 100vh;
  gap: var(--spacing-6);
}

.dashboard-header { grid-area: header; }
.dashboard-sidebar { grid-area: sidebar; }
.dashboard-main { grid-area: main; }
.dashboard-aside { grid-area: aside; }
.dashboard-footer { grid-area: footer; }

/* Card Grid */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: var(--spacing-6);
}

@media (max-width: 768px) {
  .dashboard-grid {
    grid-template-columns: 1fr;
    grid-template-areas:
      "header"
      "main"
      "aside"
      "sidebar"
      "footer";
  }
}
```

#### Tailwind Grid Implementation

```html
<!-- Responsive Grid -->
<div class="grid grid-cols-1 md:grid-cols-2 lg:grid-cols-3 gap-6">
  <div class="bg-white rounded-lg shadow-md p-6">Card 1</div>
  <div class="bg-white rounded-lg shadow-md p-6">Card 2</div>
  <div class="bg-white rounded-lg shadow-md p-6">Card 3</div>
</div>

<!-- Auto-fit Grid -->
<div class="grid grid-cols-[repeat(auto-fit,minmax(300px,1fr))] gap-6">
  <!-- Cards -->
</div>

<!-- Complex Dashboard Layout -->
<div class="grid grid-cols-[240px_1fr_300px] grid-rows-[auto_1fr_auto] gap-6 min-h-screen">
  <header class="col-span-3">Header</header>
  <aside>Sidebar</aside>
  <main>Main Content</main>
  <aside>Aside</aside>
  <footer class="col-span-3">Footer</footer>
</div>
```

#### Flexbox Patterns

```css
/* Center Alignment */
.flex-center {
  display: flex;
  align-items: center;
  justify-content: center;
}

/* Space Between */
.flex-space-between {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--spacing-4);
}

/* Vertical Stack */
.flex-stack {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-4);
}

/* Horizontal Scroll */
.flex-scroll {
  display: flex;
  gap: var(--spacing-4);
  overflow-x: auto;
  scroll-snap-type: x mandatory;
  -webkit-overflow-scrolling: touch;
}

.flex-scroll > * {
  scroll-snap-align: start;
  flex-shrink: 0;
}
```

### 6. Responsive Design

#### Mobile-First Breakpoints

```css
/* Mobile-First Breakpoint Scale */
/* Base: Mobile First (0px+) */

/* Small: 640px+ */
@media (min-width: 640px) {
  .container {
    max-width: 640px;
  }
}

/* Medium: 768px+ */
@media (min-width: 768px) {
  .container {
    max-width: 768px;
  }
}

/* Large: 1024px+ */
@media (min-width: 1024px) {
  .container {
    max-width: 1024px;
  }
}

/* XLarge: 1280px+ */
@media (min-width: 1280px) {
  .container {
    max-width: 1280px;
  }
}

/* 2XLarge: 1536px+ */
@media (min-width: 1536px) {
  .container {
    max-width: 1536px;
  }
}
```

#### Tailwind Responsive Utilities

```html
<!-- Responsive Typography -->
<h1 class="text-2xl sm:text-3xl md:text-4xl lg:text-5xl">
  Responsive Heading
</h1>

<!-- Responsive Spacing -->
<div class="p-4 sm:p-6 md:p-8 lg:p-12">
  Content
</div>

<!-- Responsive Grid -->
<div class="grid grid-cols-1 sm:grid-cols-2 lg:grid-cols-4 gap-4">
  <!-- Cards -->
</div>

<!-- Hide/Show at Breakpoints -->
<div class="hidden md:block">
  Desktop Only
</div>

<div class="block md:hidden">
  Mobile Only
</div>
```

### 7. Design Styles

#### Glassmorphism

```css
/* Glassmorphism Effect */
.glass {
  background: rgba(255, 255, 255, 0.1);
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);
  border: 1px solid rgba(255, 255, 255, 0.2);
  border-radius: var(--radius-xl);
}

.glass-dark {
  background: rgba(0, 0, 0, 0.2);
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);
  border: 1px solid rgba(255, 255, 255, 0.1);
}

/* Tailwind Implementation */
<div class="bg-white/10 backdrop-blur-md border border-white/20 rounded-2xl">
  Glassmorphism Card
</div>
```

#### Neumorphism

```css
/* Neumorphism (Soft UI) */
.neu-flat {
  background: #e0e5ec;
  border-radius: var(--radius-xl);
  box-shadow:
    20px 20px 60px #bebebe,
    -20px -20px 60px #ffffff;
}

.neu-pressed {
  background: #e0e5ec;
  border-radius: var(--radius-xl);
  box-shadow:
    inset 20px 20px 60px #bebebe,
    inset -20px -20px 60px #ffffff;
}

/* Tailwind Implementation */
<div class="bg-[#e0e5ec] rounded-2xl
            shadow-[20px_20px_60px_#bebebe,-20px_-20px_60px_#ffffff]">
  Neumorphic Element
</div>
```

#### Minimalism

```css
/* Minimalist Design */
.minimal {
  background: white;
  border: none;
  box-shadow: none;
  padding: var(--spacing-6);
  color: var(--color-gray-900);
}

.minimal-text {
  font-family: var(--font-body);
  font-weight: 400;
  line-height: 1.6;
  letter-spacing: 0;
}
```

#### Brutalism

```css
/* Brutalist Design */
.brutalist {
  background: var(--color-primary-600);
  color: white;
  border: 4px solid black;
  box-shadow: 8px 8px 0 black;
  padding: var(--spacing-6);
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.brutalist-button {
  background: var(--color-warning);
  border: 3px solid black;
  box-shadow: 4px 4px 0 black;
  transition: none;
}

.brutalist-button:hover {
  transform: translate(2px, 2px);
  box-shadow: 2px 2px 0 black;
}

.brutalist-button:active {
  transform: translate(4px, 4px);
  box-shadow: none;
}

/* Tailwind Implementation */
<button class="bg-yellow-500 text-black font-bold uppercase
               border-4 border-black shadow-[8px_8px_0_#000]
               hover:translate-x-1 hover:translate-y-1 hover:shadow-[6px_6px_0_#000]
               active:translate-x-2 active:translate-y-2 active:shadow-none
               transition-none">
  Brutalist Button
</button>
```

### 8. Accessibility (WCAG 2.1)

#### Semantic HTML Structure

```html
<!-- Proper Heading Hierarchy -->
<header>
  <h1>Main Page Title</h1>
</header>

<main>
  <section aria-labelledby="section-1-heading">
    <h2 id="section-1-heading">Section Title</h2>
    <article>
      <h3>Article Title</h3>
      <p>Article content...</p>
    </article>
  </section>
</main>

<nav aria-label="Main navigation">
  <ul>
    <li><a href="/">Home</a></li>
    <li><a href="/about">About</a></li>
  </ul>
</nav>

<footer>
  <p>&copy; 2024 Company</p>
</footer>
```

#### ARIA Labels and Roles

```html
<!-- Accessible Buttons -->
<button aria-label="Close dialog" onclick="closeDialog()">
  <svg aria-hidden="true" focusable="false">
    <use xlink:href="#icon-x"/>
  </svg>
</button>

<!-- Accessible Form Inputs -->
<label for="search">Search</label>
<input
  type="search"
  id="search"
  name="search"
  aria-describedby="search-hint"
/>
<span id="search-hint" class="sr-only">
  Search for products by name or SKU
</span>

<!-- Accessible Dropdown -->
<div class="dropdown">
  <button
    id="menu-button"
    aria-haspopup="true"
    aria-expanded="false"
    aria-controls="menu-list"
  >
    Options
  </button>
  <ul
    id="menu-list"
    role="menu"
    aria-labelledby="menu-button"
  >
    <li role="none">
      <a role="menuitem" href="/option1">Option 1</a>
    </li>
  </ul>
</div>

<!-- Screen Reader Only -->
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border-width: 0;
}
```

#### Keyboard Navigation

```css
/* Focus Visible Indicator */
*:focus-visible {
  outline: 2px solid var(--color-primary-600);
  outline-offset: 2px;
}

/* Skip Link */
.skip-link {
  position: absolute;
  top: -40px;
  left: 0;
  background: var(--color-primary-600);
  color: white;
  padding: var(--spacing-2) var(--spacing-4);
  z-index: 9999;
}

.skip-link:focus {
  top: 0;
}

/* Tab Order */
.tab-trigger {
  cursor: pointer;
}

.tab-trigger[aria-selected="true"] {
  background: var(--color-primary-600);
  color: white;
}
```

#### Color Contrast Standards

```css
/* Minimum Contrast Ratios (WCAG 2.1) */
/* AA: 4.5:1 for normal text, 3:1 for large text */
/* AAA: 7:1 for normal text, 4.5:1 for large text */

/* Example - Pass AA */
.text-primary {
  color: #2563eb; /* On white: 7.5:1 */
}

.text-secondary {
  color: #4b5563; /* On white: 5.74:1 */
}

/* Example - Fail AA */
.text-fail {
  color: #9ca3af; /* On white: 2.85:1 - FAIL */
}
```

### 9. Animation Principles

#### Micro-interactions

```css
/* Hover Animation */
.hover-lift {
  transition: transform var(--transition-base), box-shadow var(--transition-base);
}

.hover-lift:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
}

/* Focus Animation */
.focus-ring {
  transition: box-shadow var(--transition-base);
}

.focus-ring:focus {
  box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.3);
}

/* Loading Animation */
.spinner {
  width: 40px;
  height: 40px;
  border: 4px solid var(--color-gray-200);
  border-top-color: var(--color-primary-600);
  border-radius: 50%;
  animation: spin 1s linear infinite;
}

@keyframes spin {
  to { transform: rotate(360deg); }
}

/* Pulse Animation */
.pulse {
  animation: pulse 2s cubic-bezier(0.4, 0, 0.6, 1) infinite;
}

@keyframes pulse {
  0%, 100% {
    opacity: 1;
  }
  50% {
    opacity: 0.5;
  }
}
```

#### Tailwind Animations

```html
<!-- Fade In -->
<div class="animate-fade-in">
  Content fades in
</div>

<!-- Slide Up -->
<div class="animate-slide-up">
  Content slides up
</div>

<!-- Custom Animation -->
<div class="hover:scale-105 transition-transform duration-200">
  Hover to scale
</div>

<!-- Loading Spinner -->
<div class="w-10 h-10 border-4 border-gray-200 border-t-blue-600 rounded-full animate-spin">
</div>
```

### 10. Design Patterns

#### Card Component

```css
.card {
  background: white;
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
  padding: var(--spacing-6);
  transition: all var(--transition-base);
}

.card:hover {
  box-shadow: var(--shadow-lg);
  transform: translateY(-2px);
}

.card-header {
  display: flex;
  align-items: center;
  gap: var(--spacing-4);
  margin-bottom: var(--spacing-4);
}

.card-title {
  font-size: var(--text-lg);
  font-weight: 600;
  color: var(--color-gray-900);
}

.card-body {
  color: var(--color-gray-600);
  line-height: 1.6;
}

.card-footer {
  display: flex;
  gap: var(--spacing-2);
  margin-top: var(--spacing-6);
}
```

#### Modal Component

```css
.modal-backdrop {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.5);
  backdrop-filter: blur(4px);
  z-index: var(--z-modal-backdrop);
  animation: fadeIn 0.2s ease-out;
}

.modal {
  position: fixed;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  background: white;
  border-radius: var(--radius-xl);
  box-shadow: var(--shadow-xl);
  z-index: var(--z-modal);
  max-width: 500px;
  width: 90%;
  max-height: 90vh;
  overflow: auto;
  animation: scaleIn 0.2s ease-out;
}

.modal-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--spacing-6);
  border-bottom: 1px solid var(--color-gray-200);
}

.modal-body {
  padding: var(--spacing-6);
}

.modal-footer {
  display: flex;
  gap: var(--spacing-3);
  justify-content: flex-end;
  padding: var(--spacing-6);
  border-top: 1px solid var(--color-gray-200);
}
```

#### Navigation Component

```css
.navbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--spacing-4) var(--spacing-6);
  background: white;
  border-bottom: 1px solid var(--color-gray-200);
  position: sticky;
  top: 0;
  z-index: var(--z-sticky);
}

.navbar-brand {
  font-size: var(--text-xl);
  font-weight: 700;
  color: var(--color-primary-600);
}

.navbar-menu {
  display: flex;
  gap: var(--spacing-6);
}

.navbar-link {
  color: var(--color-gray-600);
  text-decoration: none;
  font-weight: 500;
  transition: color var(--transition-fast);
}

.navbar-link:hover,
.navbar-link.active {
  color: var(--color-primary-600);
}
```

### 11. Dashboard Design

#### Dashboard Layout Pattern

```css
.dashboard {
  display: grid;
  grid-template-columns: 260px 1fr;
  min-height: 100vh;
}

.dashboard-sidebar {
  background: var(--color-gray-900);
  color: white;
  padding: var(--spacing-6);
}

.dashboard-main {
  background: var(--color-gray-50);
  padding: var(--spacing-6);
}

.stat-card {
  background: white;
  padding: var(--spacing-6);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
}

.stat-value {
  font-size: var(--text-3xl);
  font-weight: 700;
  color: var(--color-gray-900);
}

.stat-label {
  font-size: var(--text-sm);
  color: var(--color-gray-600);
  margin-top: var(--spacing-2);
}
```

#### Tailwind Dashboard

```html
<div class="flex min-h-screen">
  <!-- Sidebar -->
  <aside class="w-64 bg-gray-900 text-white p-6">
    <div class="text-xl font-bold mb-8">Dashboard</div>
    <nav class="space-y-2">
      <a href="#" class="block px-4 py-2 rounded-lg bg-blue-600">Overview</a>
      <a href="#" class="block px-4 py-2 rounded-lg hover:bg-gray-800">Analytics</a>
      <a href="#" class="block px-4 py-2 rounded-lg hover:bg-gray-800">Settings</a>
    </nav>
  </aside>

  <!-- Main Content -->
  <main class="flex-1 bg-gray-50 p-6">
    <!-- Stats Grid -->
    <div class="grid grid-cols-1 md:grid-cols-2 lg:grid-cols-4 gap-6 mb-8">
      <div class="bg-white p-6 rounded-lg shadow-sm">
        <div class="text-3xl font-bold text-gray-900">1,234</div>
        <div class="text-sm text-gray-600 mt-2">Total Users</div>
      </div>
      <!-- More stats -->
    </div>
  </main>
</div>
```

### 12. E-commerce Design

#### Product Card Pattern

```css
.product-card {
  background: white;
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
  overflow: hidden;
  transition: all var(--transition-base);
}

.product-card:hover {
  box-shadow: var(--shadow-lg);
  transform: translateY(-4px);
}

.product-image {
  width: 100%;
  aspect-ratio: 1;
  object-fit: cover;
}

.product-info {
  padding: var(--spacing-4);
}

.product-name {
  font-size: var(--text-base);
  font-weight: 600;
  color: var(--color-gray-900);
  margin-bottom: var(--spacing-2);
}

.product-price {
  font-size: var(--text-lg);
  font-weight: 700;
  color: var(--color-primary-600);
}

.product-button {
  width: 100%;
  margin-top: var(--spacing-4);
}
```

### 13. Decision Trees

#### Layout Selection

```
Need to arrange content?
│
├─ Single column? → Flex column
├─ Two columns? → Grid 2 cols
├─ Three+ columns? → Grid auto-fit
├─ Complex dashboard? → Grid with named areas
└─ Horizontal scroll? → Flex with overflow
```

#### Component Style Selection

```
What's the product type?
│
├─ SaaS/B2B → Minimalism, clean borders
├─ E-commerce → Card-based, clear CTAs
├─ Creative portfolio → Glassmorphism, bold colors
├─ Developer tools → Brutalism, monospace
└─ Healthcare → Clean, high contrast, accessible
```

#### Color Scheme Selection

```
What's the brand personality?
│
├─ Trustworthy → Blue primary
├─ Energetic → Orange/Yellow primary
├─ Natural → Green primary
├─ Luxury → Black/Gold or Purple
└─ Playful → Multicolor, gradients
```

### 14. Anti-Patterns to Avoid

1. **Magic Numbers**: Never use arbitrary pixel values. Use spacing scale.
2. **Hard-coded Colors**: Never use hex codes directly. Use design tokens.
3. **Missing Focus States**: Always provide keyboard navigation indicators.
4. **Poor Contrast**: Always test contrast ratios (minimum 4.5:1).
5. **Infinite Scrolling without Pagination**: Provide alternative navigation.
6. **Tiny Touch Targets**: Buttons minimum 44x44px for mobile.
7. **Missing Loading States**: Always provide feedback for async actions.
8. **Inconsistent Spacing**: Use spacing scale consistently.
9. **Overriding Accessibility**: Never remove native accessibility features.
10. **Blocking Mobile**: Always design mobile-first.

### 15. Quality Checklist

Before delivery, verify:

- [ ] All colors use design tokens (no hardcoded hex)
- [ ] Typography follows type scale
- [ ] Spacing uses spacing scale
- [ ] All interactive elements have hover/focus/active states
- [ ] All images have alt text or are decorative
- [ ] Color contrast meets WCAG AA (4.5:1 minimum)
- [ ] Keyboard navigation works for all interactive elements
- [ ] Focus indicators are visible
- [ ] Forms have proper labels and error messages
- [ ] Loading states provided for async actions
- [ ] Responsive design tested on mobile/tablet/desktop
- [ ] Dark mode preserves contrast and readability
- [ ] Animations have `prefers-reduced-motion` support
- [ ] Touch targets minimum 44x44px on mobile
- [ ] Semantic HTML used (headings, landmarks, lists)
- [ ] ARIA labels provided where needed
- [ ] Z-index follows defined scale
- [ ] Border radius consistent within component
- [ ] Shadows follow defined scale
- [ ] Transitions follow timing standards

### 16. Quick Reference

#### Tailwind Common Patterns

```html
<!-- Container -->
<div class="container mx-auto px-4 max-w-7xl">

<!-- Flex Center -->
<div class="flex items-center justify-center">

<!-- Grid Responsive -->
<div class="grid grid-cols-1 md:grid-cols-2 lg:grid-cols-3 gap-6">

<!-- Card -->
<div class="bg-white rounded-lg shadow-md p-6 hover:shadow-lg transition-shadow">

<!-- Button Primary -->
<button class="px-6 py-3 bg-blue-600 text-white rounded-lg hover:bg-blue-700 focus:ring-2 focus:ring-blue-500">

<!-- Input -->
<input class="w-full px-4 py-3 border border-gray-300 rounded-lg focus:ring-2 focus:ring-blue-500 focus:border-transparent">

<!-- Modal Backdrop -->
<div class="fixed inset-0 bg-black/50 backdrop-blur-sm flex items-center justify-center">

<!-- Responsive Hide/Show -->
<div class="hidden md:block">Desktop only</div>
```

This comprehensive skill definition provides complete guidance for UI/UX design across modern web applications, with real code examples for every pattern.