<objective> Documents responsive design utilities in Tailwind CSS v4: the default breakpoint scale (`sm`/`md`/`lg`/`xl`/`2xl`), defining custom breakpoints via `@theme`, container queries (`@container`, `@md`, `@lg` container-relative variants), and the mobile-first authoring pattern (base styles first, larger-breakpoint overrides layered on top). </objective>

Responsive Design

Default Breakpoints

| Variant | Size | CSS | |---------|--------|-----| | sm: | 40rem (640px) | @media (width >= 40rem) | | md: | 48rem (768px) | @media (width >= 48rem) | | lg: | 64rem (1024px) | @media (width >= 64rem) | | xl: | 80rem (1280px) | @media (width >= 80rem) | | 2xl: | 96rem (1536px) | @media (width >= 96rem) |

Custom breakpoint

@theme {
  --breakpoint-3xl: 120rem;
}
/* Usage: 3xl:grid-cols-6 */

Container Queries v4

<div class="@container">
  <div class="@md:grid-cols-2 @lg:grid-cols-3">
    <!-- Responsive to container -->
  </div>
</div>

Mobile-first

<div class="text-sm md:text-base lg:text-lg">
  <!-- Small screens first -->
</div>