Prefer Container Queries

Components should respond to the space they are in, not to the viewport. A card that lives in a sidebar has maybe 300px of width even on a huge screen, and a viewport breakpoint like md:flex-row will get that wrong every time. Container queries fix this: the component asks "how wide am I?" instead of "how wide is the window?".

When writing responsive Tailwind, default to container queries. Viewport breakpoints are the exception, not the rule.

How it works

Mark the parent as a container, then use @-prefixed variants on its children:

<div class="@container">
  <div class="flex flex-col @md:flex-row @md:gap-6">
    <img class="w-full @md:w-48" />
    <div class="@md:flex-1">...</div>
  </div>
</div>

@md: here means "when the container is at least 28rem wide", regardless of viewport size. This card works in a sidebar, a modal, and a full-width grid without changing a single class.

Two rules that trip people up:

1. The @container class goes on the parent. The @md: variants go on descendants. An element cannot query its own size.
2. Container variants respond to the nearest ancestor with @container. If styles are not applying, check which container you are actually querying.

Variants

Tailwind v4 ships container queries in core. The sizes:

Also available:

• @max-md: styles below a container size.
• @min-[475px]: arbitrary values when the scale does not fit.
• @container/sidebar plus @md/sidebar:flex-row to name a container and query it from deeper in the tree, past other containers.

The full docs for this can be found here.

On Tailwind v3, the same syntax needs the @tailwindcss/container-queries plugin. Check the Tailwind version before writing classes.

When viewport breakpoints are still right

Do not convert these:

• Page-level layout. The overall grid, whether the sidebar exists at all, header and navigation behavior. These genuinely depend on the viewport.
• Fixed or sticky elements positioned relative to the viewport, like a bottom bar that becomes a side rail.
• Global typography scale tied to screen size.

Everything inside those layout regions, meaning cards, forms, media objects, stat blocks, table-to-list switches, should use container queries.

Migrating existing code

1. Find the component's responsive classes (sm:, md:, lg:).
2. Add @container to the component's root or the wrapper that owns the available space.
3. Replace viewport variants with the container variant that matches the actual width where the layout should change. Do not map md: to @md: blindly; md is 768px of viewport, @md is 448px of container. Resize the container, not the window, to find the real breakpoint.
4. Test the component in its narrowest real context (sidebar, drawer, small grid cell), not just at mobile viewport widths.

Mistakes to catch in review

• md:flex-row on a component that is rendered inside a sidebar or modal. It will stay stacked or break depending on the viewport, not its actual space.
• @md: variants used with no @container ancestor. They silently never apply.
• @container and a @md: variant on the same element. The element cannot query itself; move the variant to a child or the container class to the parent.
• A component that only looks right at the exact spot it was built for. If moving it to a different column breaks it, it is viewport-coupled.