mobile-ux-optimizer

---
name: mobile-ux-optimizer
description: Mobile-first UX optimization for touch interfaces, responsive layouts, and performance. Use for viewport handling, touch targets, gestures, mobile navigation. Activate on mobile, touch, responsive,
license: MIT
---

# Mobile-First UX Optimization

Build touch-optimized, performant mobile experiences with proper viewport handling and responsive patterns.

## When to Use

✅ **USE this skill for:**
- Viewport issues (`100vh` problems, safe areas, notches)
- Touch target sizing and spacing
- Mobile navigation patterns (bottom nav, drawers, hamburger menus)
- Swipe gestures and pull-to-refresh
- Responsive breakpoint strategies
- Mobile performance optimization

❌ **DO NOT use for:**
- Native app development → use `react-native` or `swift-executor` skills
- Desktop-only features → no skill needed, standard patterns apply
- General CSS/Tailwind questions → use Tailwind docs or `web-design-expert`
- PWA installation/service workers → use `pwa-expert` skill

## Core Principles

### Mobile-First Means Build Up, Not Down

```css
/* ❌ ANTI-PATTERN: Desktop-first (scale down) */
.card { width: 400px; }
@media (max-width: 768px) { .card { width: 100%; } }

/* ✅ CORRECT: Mobile-first (scale up) */
.card { width: 100%; }
@media (min-width: 768px) { .card { width: 400px; } }
```

### The 44px Rule

Apple's Human Interface Guidelines specify **44×44 points** as minimum touch target. Google Material suggests **48×48dp**.

```tsx
// Touch-friendly button
<button className="min-h-[44px] min-w-[44px] px-4 py-3">
  Tap me
</button>

// Touch-friendly link with adequate padding
<a href="/page" className="inline-block py-3 px-4">
  Link text
</a>
```

## Viewport Handling

### The `dvh` Solution

Mobile browsers have dynamic toolbars. `100vh` includes the URL bar, causing content to be cut off.

```css
/* ❌ ANTI-PATTERN: Content hidden behind browser UI */
.full-screen { height: 100vh; }

/* ✅ CORRECT: Responds to browser chrome */
.full-screen { height: 100dvh; }

/* Fallback for older browsers */
.full-screen {
  height: 100vh;
  height: 100dvh;
}
```

### Safe Area Insets (Notches & Home Indicators)

```css
/* Handle iPhone notch and home indicator */
.bottom-nav {
  padding-bottom: env(safe-area-inset-bottom, 0);
}

.header {
  padding-top: env(safe-area-inset-top, 0);
}

/* Full safe area padding */
.safe-container {
  padding: env(safe-area-inset-top)
           env(safe-area-inset-right)
           env(safe-area-inset-bottom)
           env(safe-area-inset-left);
}
```

**Required meta tag:**
```html
<meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover">
```

### Tailwind Safe Area Classes

```tsx
// Custom Tailwind utilities (add to globals.css)
@layer utilities {
  .pb-safe { padding-bottom: env(safe-area-inset-bottom); }
  .pt-safe { padding-top: env(safe-area-inset-top); }
  .h-screen-safe { height: calc(100dvh - env(safe-area-inset-top) - env(safe-area-inset-bottom)); }
}

// Usage
<nav className="fixed bottom-0 pb-safe bg-leather-900">
  <BottomNav />
</nav>
```

## Mobile Navigation Patterns

### Bottom Navigation (Recommended for Mobile)

```tsx
// components/BottomNav.tsx
'use client';

import { usePathname } from 'next/navigation';
import Link from 'next/link';

const navItems = [
  { href: '/', icon: HomeIcon, label: 'Home' },
  { href: '/meetings', icon: CalendarIcon, label: 'Meetings' },
  { href: '/tools', icon: ToolsIcon, label: 'Tools' },
  { href: '/my', icon: UserIcon, label: 'My Recovery' },
];

export function BottomNav() {
  const pathname = usePathname();

  return (
    <nav className="fixed bottom-0 left-0 right-0 bg-leather-900 border-t border-leather-700 pb-safe">
      <div className="flex justify-around">
        {navItems.map(({ href, icon: Icon, label }) => {
          const isActive = pathname === href || pathname.startsWith(`${href}/`);
          return (
            <Link
              key={href}
              href={href}
              className={`
                flex flex-col items-center py-2 px-3 min-h-[56px] min-w-[64px]
                ${isActive ? 'text-ember-400' : 'text-leather-400'}
              `}
            >
              <Icon className="w-6 h-6" />
              <span className="text-xs mt-1">{label}</span>
            </Link>
          );
        })}
      </div>
    </nav>
  );
}
```

### Slide-Out Drawer (Side Menu)

```tsx
'use client';

import { useState, useEffect } from 'react';
import { createPortal } from 'react-dom';

interface DrawerProps {
  isOpen: boolean;
  onClose: () => void;
  children: React.ReactNode;
}

export function Drawer({ isOpen, onClose, children }: DrawerProps) {
  // Prevent body scroll when open
  useEffect(() => {
    if (isOpen) {
      document.body.style.overflow = 'hidden';
    }
    return () => {
      document.body.style.overflow = '';
    };
  }, [isOpen]);

  // Close on escape
  useEffect(() => {
    const handleEscape = (e: KeyboardEvent) => {
      if (e.key === 'Escape') onClose();
    };
    document.addEventListener('keydown', handleEscape);
    return () => document.removeEventListener('keydown', handleEscape);
  }, [onClose]);

  if (!isOpen) return null;

  return createPortal(
    <div className="fixed inset-0 z-50">
      {/* Backdrop */}
      <div
        className="absolute inset-0 bg-black/60 backdrop-blur-sm"
        onClick={onClose}
        aria-hidden="true"
      />

      {/* Drawer */}
      <div
        className="absolute left-0 top-0 h-full w-[280px] max-w-[80vw]
                   bg-leather-900 shadow-xl transform transition-transform
                   animate-slide-in-left"
        role="dialog"
        aria-modal="true"
      >
        <div className="h-full overflow-y-auto pt-safe pb-safe">
          {children}
        </div>
      </div>
    </div>,
    document.body
  );
}
```

## Touch Gestures

> **Full implementations in `references/gestures.md`**

| Hook | Purpose |
|------|---------|
| `useSwipe()` | Directional swipe detection with configurable threshold |
| `usePullToRefresh()` | Pull-to-refresh with visual feedback and resistance |

**Quick usage:**

```tsx
// Swipe to dismiss
const { handleTouchStart, handleTouchEnd } = useSwipe({
  onSwipeLeft: () => dismiss(),
  threshold: 50,
});

// Pull to refresh
const { containerRef, pullDistance, isRefreshing, handlers } = 
  usePullToRefresh(async () => await refetchData());
```

## Mobile Performance

### Image Optimization

```tsx
import Image from 'next/image';

// Responsive images with proper sizing
<Image
  src="/hero.jpg"
  alt="Hero"
  fill
  sizes="(max-width: 768px) 100vw, 50vw"
  priority // For above-the-fold images
  className="object-cover"
/>

// Lazy load below-fold images
<Image
  src="/feature.jpg"
  alt="Feature"
  width={400}
  height={300}
  loading="lazy"
/>
```

### Reduce Bundle Size

```tsx
// Dynamic imports for heavy components
const HeavyChart = dynamic(() => import('@/components/Chart'), {
  loading: () => <ChartSkeleton />,
  ssr: false, // Skip server render for client-only
});

// Lazy load below-fold sections
const Comments = dynamic(() => import('@/components/Comments'));
```

### Skeleton Screens (Not Spinners)

```tsx
// Skeleton that matches final content layout
function MeetingCardSkeleton() {
  return (
    <div className="p-4 bg-leather-800 rounded-lg animate-pulse">
      <div className="h-4 bg-leather-700 rounded w-3/4 mb-2" />
      <div className="h-3 bg-leather-700 rounded w-1/2 mb-4" />
      <div className="flex gap-2">
        <div className="h-6 w-16 bg-leather-700 rounded" />
        <div className="h-6 w-16 bg-leather-700 rounded" />
      </div>
    </div>
  );
}

// Usage
{isLoading ? (
  <div className="space-y-4">
    {[...Array(5)].map((_, i) => <MeetingCardSkeleton key={i} />)}
  </div>
) : (
  meetings.map(m => <MeetingCard key={m.id} meeting={m} />)
)}
```

## Responsive Patterns

### Tailwind Breakpoint Strategy

```
sm: 640px   - Large phones (landscape)
md: 768px   - Tablets
lg: 1024px  - Small laptops
xl: 1280px  - Desktops
2xl: 1536px - Large screens
```

```tsx
// Mobile: stack, Tablet+: side-by-side
<div className="flex flex-col md:flex-row gap-4">
  <aside className="w-full md:w-64">Sidebar</aside>
  <main className="flex-1">Content</main>
</div>

// Mobile: bottom nav, Desktop: sidebar
<nav className="md:hidden fixed bottom-0 left-0 right-0">
  <BottomNav />
</nav>
<aside className="hidden md:block w-64">
  <SidebarNav />
</aside>
```

### Container Queries (CSS-only Responsive Components)

```css
/* Component responds to its container, not viewport */
@container (min-width: 400px) {
  .card { flex-direction: row; }
}
```

```tsx
<div className="@container">
  <div className="flex flex-col @md:flex-row">
    {/* Responds to parent container width */}
  </div>
</div>
```

## Testing on Real Devices

### Chrome DevTools Mobile Emulation
1. Open DevTools (F12)
2. Toggle device toolbar (Ctrl+Shift+M)
3. Select device or set custom dimensions
4. **Throttle network/CPU** for realistic performance

### Must-Test Scenarios
- [ ] Content doesn't get cut off by notch/home indicator
- [ ] Touch targets are at least 44×44px
- [ ] Scrolling is smooth (no jank)
- [ ] Bottom nav doesn't block content
- [ ] Forms work with virtual keyboard visible
- [ ] Landscape orientation works
- [ ] Pull-to-refresh doesn't fight with scroll

### BrowserStack/Real Device Testing
```bash
# Expose local dev server to internet
npx localtunnel --port 3000
# or
ngrok http 3000
```

## Quick Reference

| Issue | Solution |
|-------|----------|
| Content cut off at bottom | Use `100dvh` instead of `100vh` |
| Notch overlaps content | Add `pt-safe` / `pb-safe` |
| Touch targets too small | Min 44×44px |
| Scroll locked | Check `overflow: hidden` on body |
| Keyboard covers input | Use `visualViewport` API |
| Janky scrolling | Use `will-change: transform` |
| Double-tap zoom | Add `touch-action: manipulation` |

## References

See `/references/` for detailed guides:
- `keyboard-handling.md` - Virtual keyboard and form UX
- `animations.md` - Touch-friendly animations
- `accessibility.md` - Mobile a11y requirements