mobile-ui-design

name	mobile-ui-design
description	Mobile-first interface design for touch-optimized, native-feeling web and app UIs. Trigger: user asks to "design for mobile", "build a mobile UI", "make it mobile-friendly", "create a mobile app", "build a responsive mobile layout", "design a bottom sheet", "mobile navigation", or any mobile-specific interface work.
license	MIT

Mobile UI Design

Pre-Flight: Check Design Context

Before generating mobile UI code:

1. Use get_design_context to check for existing design tokens, platform guidelines, or component libraries.
2. If a Figma URL is provided, pull screenshots and metadata to match the design.
3. Determine: Is this a native app (React Native/Flutter), a PWA, or a responsive website?

---

1. Touch Target Sizes

Every interactive element must be large enough to tap reliably.

Minimum Sizes

Platform	Minimum Target	Recommended
Apple HIG	44x44px	48x48px
Material Design	48x48px	56x56px
WCAG 2.5.8	24x24px (AAA: 44px)	44x44px

Implementation

/* Ensure tap targets even on small visual elements */
.icon-button {
  width: 24px;
  height: 24px;
  /* Expand tap target with padding or pseudo-element */
  position: relative;
}
.icon-button::after {
  content: '';
  position: absolute;
  inset: -12px; /* extends tap area to 48x48 */
}

Spacing Between Targets

Minimum 8px gap between tappable elements. 12px+ is preferred. This prevents accidental taps.

---

2. Bottom Navigation

The thumb reaches the bottom of the screen most easily. Put primary navigation there.

Standard Bottom Tab Bar

<nav class="fixed bottom-0 inset-x-0 bg-white border-t border-gray-200
  safe-area-bottom z-50">
  <div class="flex items-center justify-around h-16">
    <!-- Active tab -->
    <a href="#" class="flex flex-col items-center gap-0.5 text-indigo-600 min-w-[64px]">
      <svg class="w-6 h-6" fill="currentColor"><!-- home icon --></svg>
      <span class="text-[10px] font-medium">Home</span>
    </a>
    <!-- Inactive tab -->
    <a href="#" class="flex flex-col items-center gap-0.5 text-gray-400 min-w-[64px]">
      <svg class="w-6 h-6" fill="none" stroke="currentColor"><!-- search icon --></svg>
      <span class="text-[10px] font-medium">Search</span>
    </a>
    <!-- ... 3-5 tabs total -->
  </div>
</nav>

Rules

• Maximum 5 tabs. 3–4 is ideal.
• Active tab: filled icon + primary color. Inactive: outline icon + gray.
• Labels are required. Icon-only tabs have poor discoverability.
• Never use a hamburger menu as a tab bar replacement.
• Account for bottom safe area on notched devices.

Safe Area CSS

.safe-area-bottom {
  padding-bottom: env(safe-area-inset-bottom);
}

---

3. Gesture-Friendly Interactions

Swipe Actions

<!-- Swipe-to-reveal pattern (conceptual structure) -->
<div class="relative overflow-hidden">
  <!-- Background action (revealed on swipe) -->
  <div class="absolute inset-y-0 right-0 flex items-center bg-red-500 px-6">
    <span class="text-white font-medium">Delete</span>
  </div>
  <!-- Foreground content (swipeable) -->
  <div class="bg-white px-4 py-3 transform transition-transform touch-pan-y">
    <div class="font-medium text-gray-900">List Item</div>
    <div class="text-sm text-gray-500">Swipe left for actions</div>
  </div>
</div>

Pull-to-Refresh

• Indicator appears at top as user pulls down.
• Use a spinner or custom animation.
• Trigger refresh at ~80px pull distance.
• Provide haptic feedback if possible (native only).

Common Mobile Gestures

Gesture	Use Case	Implementation
Swipe left/right	Reveal actions, navigate	touch-action: pan-y
Pull down	Refresh content	Overscroll detection
Long press	Context menu, reorder	@touchstart with timeout
Pinch	Zoom images/maps	touch-action: manipulation
Swipe up	Dismiss sheet, expand	Drag handle on bottom sheet

---

4. iOS vs Android Design Language

Key Differences

Element	iOS (Human Interface)	Android (Material)
Navigation	Tab bar at bottom	Bottom navigation bar
Back	Swipe from left edge / text "Back"	Arrow icon top-left
Titles	Large title that collapses	Centered or left-aligned
Buttons	Rounded rect, no elevation	Rounded, with elevation
Switches	Green/white toggle	Track + thumb with ripple
Sheets	Rounded top, drag handle	Full-width, drag handle
Typography	SF Pro (system)	Roboto (system)
Spacing	16px margins	16px margins

Cross-Platform Approach

When building for both, lean toward iOS patterns for polish and Material patterns for interaction feedback. Use system fonts:

font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;

---

5. Safe Areas

Device Considerations

/* Status bar area */
.top-safe {
  padding-top: env(safe-area-inset-top);
}

/* Home indicator / gesture bar */
.bottom-safe {
  padding-bottom: env(safe-area-inset-bottom);
}

/* Notch / Dynamic Island on landscape */
.side-safe {
  padding-left: env(safe-area-inset-left);
  padding-right: env(safe-area-inset-right);
}

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

Viewport Meta

<meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover" />

The viewport-fit=cover is required for env(safe-area-inset-*) to work.

---

6. Mobile Typography Scale

Recommended Scale

Role	Size	Weight	Line Height
Large title	34px	700	1.2
Title 1	28px	700	1.2
Title 2	22px	700	1.25
Title 3	20px	600	1.25
Headline	17px	600	1.3
Body	17px	400	1.5
Callout	16px	400	1.4
Subhead	15px	400	1.4
Footnote	13px	400	1.3
Caption	12px	400	1.3

Rules

• Body text minimum 16px on mobile (prevents iOS zoom on input focus).
• Line length: 35–50 characters max for comfortable mobile reading.
• Use rem units based on 16px root.

---

7. Thumb Zone Optimization

The Thumb Zone Map

+-----------------------------+
|     Hard to reach           |  <- Top 25%: Put secondary actions, titles
|                             |
|-----------------------------|
|     Comfortable stretch     |  <- Middle 50%: Content, scrollable lists
|                             |
|-----------------------------|
|     Easy / Natural          |  <- Bottom 25%: Primary actions, nav, FAB
+-----------------------------+

Practical Rules

• Primary actions at bottom: CTA buttons, submit buttons, navigation.
• Search bars: Consider bottom placement (like iOS Safari).
• FAB (Floating Action Button): Bottom-right corner, 56px, with shadow.
• Destructive actions at top: Harder to reach = harder to accidentally trigger.

<!-- Bottom-anchored CTA -->
<div class="fixed bottom-0 inset-x-0 p-4 bg-gradient-to-t from-white via-white
  to-transparent pt-12 safe-area-bottom">
  <button class="w-full bg-indigo-600 text-white py-4 rounded-2xl font-semibold
    text-lg active:bg-indigo-700 transition-colors">
    Continue
  </button>
</div>

---

8. Sheet / Bottom Drawer Patterns

Bottom Sheet Structure

<div class="fixed inset-0 z-50">
  <!-- Backdrop -->
  <div class="absolute inset-0 bg-black/40 backdrop-blur-sm"></div>

  <!-- Sheet -->
  <div class="absolute bottom-0 inset-x-0 bg-white rounded-t-3xl
    max-h-[85vh] overflow-y-auto safe-area-bottom">
    <!-- Drag handle -->
    <div class="flex justify-center pt-3 pb-2">
      <div class="w-10 h-1 rounded-full bg-gray-300"></div>
    </div>

    <!-- Content -->
    <div class="px-4 pb-6">
      <h2 class="text-xl font-bold text-gray-900 mb-4">Sheet Title</h2>
      <!-- Sheet content -->
    </div>
  </div>
</div>

Sheet Variants

• Peek sheet: Shows 30% of content, drag to expand.
• Action sheet: List of options (iOS-style).
• Full-screen sheet: Slides up to cover entire screen with close button.
• Map sheet: Persistent bottom sheet over a map (Google Maps style).

Sheet Rules

• Always include a drag handle (40px wide, 4px tall, centered, rounded).
• Max height: 85% of viewport. Let it scroll internally.
• Dismiss: swipe down, tap backdrop, or explicit close button.
• Snap points: collapsed, half, expanded.

---

9. Mobile Form Design

Rules

1. Large inputs: Minimum 48px height, 16px+ font (avoids iOS zoom).
2. Full-width inputs: Edge-to-edge within the container.
3. Smart keyboard types: Use inputmode attribute.
4. Sticky submit button: Fixed at bottom of screen.
5. Single column only: Never side-by-side fields on mobile.

Input Mode Attribute

<!-- Phone number: numeric keyboard -->
<input type="tel" inputmode="tel" />

<!-- Email: keyboard with @ and . -->
<input type="email" inputmode="email" />

<!-- Number: numeric keypad -->
<input type="text" inputmode="numeric" pattern="[0-9]*" />

<!-- URL: keyboard with / and .com -->
<input type="url" inputmode="url" />

<!-- Search: keyboard with search/go button -->
<input type="search" inputmode="search" />

Mobile-Optimized Input

<div class="space-y-1.5">
  <label for="phone" class="block text-sm font-medium text-gray-700">
    Phone number
  </label>
  <input
    type="tel"
    id="phone"
    inputmode="tel"
    autocomplete="tel"
    class="block w-full h-12 rounded-xl border border-gray-300 px-4
      text-base text-gray-900 placeholder:text-gray-400
      focus:border-indigo-500 focus:ring-2 focus:ring-indigo-500/20"
    placeholder="[phone]"
  />
</div>

---

10. Native-Feeling Animations

Timing Functions

/* iOS-like spring curve */
--ease-spring: cubic-bezier(0.175, 0.885, 0.32, 1.275);

/* Quick in, slow out (for entering elements) */
--ease-out: cubic-bezier(0.16, 1, 0.3, 1);

/* Slow in, quick out (for exiting elements) */
--ease-in: cubic-bezier(0.55, 0, 1, 0.45);

Common Transitions

/* Page transition: slide from right */
.page-enter {
  transform: translateX(100%);
  animation: slide-in 350ms var(--ease-out) forwards;
}
@keyframes slide-in {
  to { transform: translateX(0); }
}

/* Sheet reveal: slide up */
.sheet-enter {
  transform: translateY(100%);
  animation: sheet-up 400ms var(--ease-out) forwards;
}
@keyframes sheet-up {
  to { transform: translateY(0); }
}

/* Tap feedback */
.tap-feedback:active {
  transform: scale(0.97);
  opacity: 0.8;
  transition: all 50ms ease;
}

Animation Rules for Mobile

1. Keep animations under 400ms. 200–300ms feels snappy.
2. Use transform and opacity only for 60fps performance.
3. Add will-change: transform sparingly for animated elements.
4. Respect prefers-reduced-motion:

@media (prefers-reduced-motion: reduce) {
  * { animation-duration: 0.01ms !important; transition-duration: 0.01ms !important; }
}

5. Provide haptic feedback for important actions (native only).

---

Mobile Design Checklist

• All tap targets are 44px+ minimum
• Bottom navigation with 3–5 tabs and labels
• Safe areas respected (top, bottom, sides)
• Body text is 16px+ (no iOS zoom on focus)
• Primary actions are in the thumb zone (bottom)
• Forms use correct inputmode attributes
• Sheets have drag handles and dismiss gestures
• Animations are under 400ms and use GPU-friendly properties
• viewport-fit=cover meta tag is set
• prefers-reduced-motion is respected
• Content is readable at 320px width
• No horizontal scroll on any screen