frontend-responsive-design-standards

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SKILL.md

Build responsive, mobile-first layouts using fluid containers, flexible units, media queries, and touch-friendly design that works across all screen sizes. Use this skill when creating or modifying UI layouts, responsive grids, breakpoint styles, mobile navigation, or any interface that needs to adapt to different screen sizes. Apply when working with responsive CSS, media queries, viewport settings, flexbox/grid layouts, mobile-first styling, breakpoint definitions (mobile, tablet, desktop), touch target sizing, relative units (rem, em, %), image optimization for different screens, or testing layouts across multiple devices. Use for any task involving multi-device support, responsive design patterns, or adaptive layouts.

npx skills add am-will/codex-skills --skill frontend-responsive-design-standards

Documentation

SKILL.mdView source

Frontend Responsive Design Standards

Rule: Mobile-first development with consistent breakpoints, fluid layouts, relative units, and touch-friendly targets.

When to use this skill

When creating or modifying layouts that need to work on mobile, tablet, and desktop
When implementing mobile-first design patterns starting with mobile layout
When writing media queries or breakpoint-specific styles
When using flexible units (rem, em, %) instead of fixed pixels for scalability
When implementing fluid layouts with percentage-based widths or flexbox/grid
When ensuring touch targets meet minimum size requirements (44x44px) for mobile
When optimizing images and assets for different screen sizes and mobile networks
When testing UI across multiple device sizes and breakpoints
When maintaining readable typography across all screen sizes
When prioritizing content display on smaller screens through layout decisions
When using responsive design utilities in CSS frameworks (Tailwind, Bootstrap responsive classes)

This Skill provides Codex with specific guidance on how to adhere to coding standards as they relate to how it should handle frontend responsive.

Mobile-First Development - Mandatory

Always start with mobile layout, then enhance for larger screens.

Bad (desktop-first):

.container {
  width: 1200px;
  display: grid;
  grid-template-columns: repeat(

Good (mobile-first):

Why mobile-first:

Forces content prioritization
Better performance on mobile (no overriding)
Progressive enhancement over graceful degradation

Standard Breakpoints

Identify and use project breakpoints consistently:

Common breakpoint systems:

Tailwind:

Bootstrap:

Check existing codebase for breakpoint definitions before creating new ones.

Usage (Tailwind):

Usage (CSS):

Never use arbitrary breakpoints like 850px or 1150px unless explicitly required.

Fluid Layouts

Use flexible containers that adapt to screen size:

Bad (fixed widths):

Good (fluid):

Patterns for fluid layouts:

Flexbox: flex: 1, flex-grow, flex-shrink
Grid: 1fr, minmax(), auto-fit, auto-fill
Percentage widths: width: 100%, max-width: 1200px
Container queries (modern): @container (min-width: 400px)

Relative Units Over Fixed Pixels

Use rem/em for scalability and accessibility:

Bad:

Good:

When to use each unit:

rem: Font sizes, spacing, layout dimensions (scales with root font size)
em: Component-relative sizing (scales with parent font size)
%: Widths, heights relative to parent
px: Borders (1px), shadows, very small values
vw/vh: Full viewport dimensions, hero sections
ch: Text-based widths (e.g., max-width: 65ch for readable line length)

Framework utilities handle this automatically:

Touch-Friendly Design

Minimum touch target size: 44x44px (iOS) / 48x48px (Android)

Bad:

Good:

Touch target checklist:

Buttons minimum 44x44px
Links in text have adequate spacing
Form inputs have sufficient height (min 44px)
Icon buttons have padding for larger hit area
Spacing between interactive elements (min 8px)

Readable Typography

Maintain readable font sizes without zoom:

Bad:

Good:

Typography guidelines:

Body text: 16px (1rem) minimum
Small text: 14px (0.875rem) minimum
Line height: 1.5 for body, 1.2 for headings
Line length: 45-75 characters (use max-width: 65ch)
Contrast: WCAG AA minimum (4.5:1 for normal text)

Responsive typography:

Or with clamp (fluid):

Content Priority on Mobile

Show most important content first, hide or collapse secondary content:

Bad:

Good:

Strategies:

Hide non-essential elements on mobile
Use hamburger menus for navigation
Collapse accordions/tabs for secondary content
Stack layouts vertically on mobile
Use order property to reorder content

Image Optimization

Serve appropriate images for device size:

Bad:

Good:

Or with modern formats:

Framework-specific:

Testing Across Devices

Verify layouts at key breakpoints before completing work:

Test checklist:

Testing methods:

Browser DevTools responsive mode
Real device testing (iOS/Android)
Browser extensions (Responsive Viewer)
Automated visual regression tests

Common issues to check:

Horizontal scrolling on mobile
Text overflow or truncation
Overlapping elements
Unreadable font sizes
Touch targets too small
Images not loading or distorted

Common Responsive Patterns

Navigation:

Grid layouts:

Sidebar layouts:

Verification Checklist

Before completing responsive work:

Quick Reference

Situation	Action
Starting new layout	Begin with mobile (320-375px)
Need breakpoint	Use project standard (check existing code)
Setting width	Use `width: 100%` + `max-width`
Setting font size	Use `rem` (16px = 1rem)
Setting spacing	Use `rem` or framework utilities
Button too small	Ensure min 44x44px with padding
Text too small	Minimum 16px (1rem) for body
Testing layout	Check 375px, 768px, 1024px, 1440px
Images loading slow	Use srcset and modern formats

npx skills add am-will/codex-skills --skill frontend-responsive-design-standards

Documentation

SKILL.md

frontend responsive design standards | SkillBundle

.container {
  width: 100%;
  display: grid;
  grid-template-columns: 1fr;
}
 
@media (min-width: 768px) {
  .container {
    grid-template-columns: repeat(2, 1fr);
  }
}
 
@media (min-width: 1024px) {
  .container {
    max-width: 1200px;
    grid-template-columns: repeat(4, 1fr);
  }
}

sm: 640px   (small tablets)
md: 768px   (tablets)
lg: 1024px  (laptops)
xl: 1280px  (desktops)
2xl: 1536px (large desktops)

sm: 576px
md: 768px
lg: 992px
xl: 1200px
xxl: 1400px

<div className="grid grid-cols-1 md:grid-cols-2 lg:grid-cols-4">

@media (min-width: 768px) { }
@media (min-width: 1024px) { }

.container { width: 1200px; }
.sidebar { width: 300px; }
.content { width: 900px; }

.container {
  width: 100%;
  max-width: 1200px;
  padding: 0 1rem;
}
 
.layout {
  display: grid;
  grid-template-columns: 1fr;
}
 
@media (min-width: 1024px) {
  .layout {
    grid-template-columns: 300px 1fr;
  }
}

font-size: 16px;
padding: 20px;
margin: 10px;
border-radius: 8px;

font-size: 1rem;      /* 16px base */
padding: 1.25rem;     /* 20px */
margin: 0.625rem;     /* 10px */
border-radius: 0.5rem; /* 8px */

<div className="text-base p-5 m-2.5 rounded-lg">

.icon-button {
  width: 24px;
  height: 24px;
}

.icon-button {
  width: 24px;
  height: 24px;
  padding: 12px; /* Total: 48x48px */
  /* Or use min-width/min-height */
  min-width: 44px;
  min-height: 44px;
}

body { font-size: 12px; }
.small-text { font-size: 10px; }

body { font-size: 1rem; } /* 16px minimum */
.small-text { font-size: 0.875rem; } /* 14px minimum */

h1 {
  font-size: 2rem;
}
 
@media (min-width: 768px) {
  h1 {
    font-size: 2.5rem;
  }
}
 
@media (min-width: 1024px) {
  h1 {
    font-size: 3rem;
  }
}

h1 {
  font-size: clamp(2rem, 5vw, 3rem);
}

<div>
  <Sidebar /> {/* Full sidebar on mobile */}
  <MainContent />
</div>

<div className="flex flex-col lg:flex-row">
  <MainContent className="order-1" />
  <Sidebar className="order-2 hidden lg:block" />
</div>

<img src="hero-4000x3000.jpg" alt="Hero">

<img
  src="hero-800x600.jpg"
  srcset="
    hero-400x300.jpg 400w,
    hero-800x600.jpg 800w,
    hero-1600x1200.jpg 1600w
  "
  sizes="(max-width: 768px) 100vw, (max-width: 1200px) 50vw, 800px"
  alt="Hero"
>

<picture>
  <source srcset="hero.avif" type="image/avif">
  <source srcset="hero.webp" type="image/webp">
  <img src="hero.jpg" alt="Hero">
</picture>

// Next.js
<Image
  src="/hero.jpg"
  width={800}
  height={600}
  sizes="(max-width: 768px) 100vw, 50vw"
  alt="Hero"
/>

// Mobile: Hamburger menu
// Desktop: Horizontal nav
<nav className="lg:flex lg:items-center">
  <button className="lg:hidden">Menu</button>
  <ul className="hidden lg:flex lg:gap-4">
    <li>Home</li>
    <li>About</li>
  </ul>
</nav>

.grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 1rem;
}
 
@media (min-width: 640px) {
  .grid { grid-template-columns: repeat(2, 1fr); }
}
 
@media (min-width: 1024px) {
  .grid { grid-template-columns: repeat(4, 1fr); }
}

.layout {
  display: flex;
  flex-direction: column;
}
 
@media (min-width: 1024px) {
  .layout {
    flex-direction: row;
  }
  .sidebar { width: 300px; }
  .content { flex: 1; }
}