/* Base styles (mobile) */
.container {
  padding: 1rem;
}

.nav {
  display: none; /* Hidden on mobile */
}

.nav-toggle {
  display: block; /* Hamburger visible */
}

/* Tablet and up */
@media (min-width: 768px) {
  .container {
    padding: 2rem;
    max-width: 720px;
    margin: 0 auto;
  }

  .nav {
    display: flex;
  }

  .nav-toggle {
    display: none;
  }
}

/* Desktop */
@media (min-width: 1024px) {
  .container {
    max-width: 960px;
  }
}

Touch-Friendly Design

/* Minimum touch target: 48x48px */
.button {
  min-height: 48px;
  min-width: 48px;
  padding: 12px 24px;
}

/* Adequate spacing */
.list-item {
  padding: 16px;
  margin-bottom: 8px;
}

Performance Requirements

Metric	Target
First Contentful Paint	<3s on 3G
JS bundle	<100KB gzipped
Total page weight	<500KB

Progressive Enhancement

<!-- Layer 1: Semantic HTML (works without CSS/JS) -->
<nav>
  <a href="/home">Home</a>
  <a href="/about">About</a>
</nav>

<!-- Layer 2: CSS enhances appearance -->
<!-- Layer 3: JS adds interactivity -->

Best Practices

Start design at 320px width
Use relative units (rem, %, vw)
Test on real devices
Optimize images for mobile
Minimize JavaScript for initial load
Ensure readable text without zooming

Name	Width	Devices
Mobile	320-480px	iPhone SE, small Android
Tablet	481-768px	iPad mini
Desktop	769-1024px	iPad Pro, laptops
Large	1025px+	Desktop monitors

mobile-first-design

Mobile-First Design

Breakpoints

Mobile-First CSS