Responsive Design

Responsive design means building layouts that adapt to any screen size — from a phone to a widescreen monitor. The goal is one codebase that works everywhere.

The Viewport Meta Tag

This tag is required for responsive design to work on mobile devices:

<meta name="viewport" content="width=device-width, initial-scal=1.0">

Without it, mobile browsers render the page at a desktop width (typically 980px) and then zoom out, making everything tiny.

Mobile-First Approach

Write your base styles for small screens, then add complexity for larger ones. This keeps mobile styles simple and avoids overriding desktop styles on smaller devices:

/* Base: single column for mobile */
.grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 1rem;
}

/* Tablet: 2 columns */
@media (min-width: 768px) {
  .grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

/* Desktop: 3 columns */
@media (min-width: 1024px) {
  .grid {
    grid-template-columns: repeat(3, 1fr);
  }
}

Common breakpoints:

640px — small tablets, large phones in landscape
768px — tablets
1024px — small laptops
1280px — desktops

These are guidelines, not rules. Set breakpoints where your design breaks, not at specific devices.

Media Queries

Media queries conditionally apply styles based on viewport characteristics:

/* Width-based (most common) */
@media (min-width: 768px) {
  .sidebar { display: block; }
}

/* Range syntax (modern, more readable) */
@media (768px <= width < 1024px) {
  .container { max-width: 720px; }
}

/* Orientation */
@media (orientation: landscape) {
  .hero { min-height: 50dvh; }
}

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

/* Preference: dark mode */
@media (prefers-color-scheme: dark) {
  :root {
    --color-bg: #0a0a0a;
    --color-text: #e5e5e5;
  }
}

/* Hover capability — only apply hover effects on devices that support it */
@media (hover: hover) {
  .card:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
  }
}

Fluid Typography

Instead of setting fixed font sizes at breakpoints, use clamp() to create type that scales smoothly with the viewport:

h1 {
  /* Minimum 2rem, scales with viewport, maximum 4rem */
  font-size: clamp(2rem, 5vw + 1rem, 4rem);
}

p {
  font-size: clamp(1rem, 0.5vw + 0.875rem, 1.25rem);
}

The clamp(min, preferred, max) function picks the middle value, clamped between the minimum and maximum. This eliminates the need for font-size media queries in most cases.

Fluid spacing

The same technique works for spacing:

.section {
  padding: clamp(2rem, 5vw, 6rem) clamp(1rem, 3vw, 4rem);
}

.grid {
  gap: clamp(1rem, 2vw, 2rem);
}

Responsive Images

Images should never overflow their container and should load at an appropriate size:

img {
  max-width: 100%;
  height: auto;
  display: block;
}

For art direction or performance, use srcset and sizes to serve different images at different viewport widths:

<img
  src="photo-800.jpg"
  srcset="
    photo-400.jpg 400w,
    photo-800.jpg 800w,
    photo-1200.jpg 1200w
  "
  sizes="
    (min-width: 1024px) 50vw,
    100vw
  "
  alt="A landscape photo"
>

The browser picks the best image based on viewport width and device pixel ratio.

For different image crops at different sizes, use <picture>:

<picture>
  <source media="(min-width: 768px)" srcset="hero-wide.jpg">
  <source media="(min-width: 480px)" srcset="hero-medium.jpg">
  <img src="hero-small.jpg" alt="Hero image">
</picture>

Container Queries

Container queries let components respond to their parent container's size instead of the viewport. This makes components truly reusable — a card can behave differently in a sidebar versus a main content area:

/* Define a containment context */
.card-wrapper {
  container-type: inline-size;
  container-name: card;
}

/* Style the card based on its container's width */
@container card (min-width: 400px) {
  .card {
    display: flex;
    flex-direction: row;
    gap: 1rem;
  }

  .card-image {
    width: 40%;
  }
}

@container card (max-width: 399px) {
  .card {
    display: flex;
    flex-direction: column;
  }

  .card-image {
    width: 100%;
  }
}

<!-- In a narrow sidebar: card stacks vertically -->
<aside class="card-wrapper" style="width: 300px;">
  <div class="card">
    <img class="card-image" src="photo.jpg" alt="">
    <div class="card-body">
      <h3>Title</h3>
      <p>Description</p>
    </div>
  </div>
</aside>

<!-- In main content: card lays out horizontally -->
<div class="card-wrapper" style="width: 600px;">
  <div class="card">
    <img class="card-image" src="photo.jpg" alt="">
    <div class="card-body">
      <h3>Title</h3>
      <p>Description</p>
    </div>
  </div>
</div>

Responsive Layout Patterns

.layout {
  display: grid;
  grid-template-columns: 1fr;
}

@media (min-width: 768px) {
  .layout {
    grid-template-columns: 250px 1fr;
  }
}

.nav {
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  display: flex;
  justify-content: space-around;
  padding: 0.5rem;
  background: white;
  border-top: 1px solid #ddd;
}

@media (min-width: 768px) {
  .nav {
    position: static;
    border-top: none;
    justify-content: flex-end;
    gap: 2rem;
    padding: 1rem 2rem;
  }
}

Responsive text truncation

.title {
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

/* On larger screens, allow wrapping */
@media (min-width: 768px) {
  .title {
    white-space: normal;
    overflow: visible;
  }
}

Testing Responsive Designs

Browser DevTools — toggle the device toolbar to simulate different viewport sizes.
Real devices — always test on an actual phone. Emulators miss touch targets, scrolling behavior, and browser chrome.
Resize your browser window — drag the edge to see how layouts reflow. Look for awkward breaks.
Check at every width — don't just test at breakpoints. Content between breakpoints matters too.