<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

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>