LLM Best Practices

CSS: Container Queries

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Overview

A container query lets a component restyle itself from its parent’s size instead of the window’s, so one card renders correctly in a 240px sidebar and an 800px column with no conditional class strings. Size container queries have been Baseline widely available since August 2025. The umbrella page is css.

Query the container, not the viewport

Use @container when a component should respond to the space it has. Use @media for conditions about the device or user: viewport structure, touch, print, reduced motion.

.card-slot { container-type: inline-size; }
 
.card .title { font-size: 1rem; }
 
@container (min-width: 32rem) {
  .card { display: grid; grid-template-columns: 12rem 1fr; }
  .card .title { font-size: 1.25rem; }
}

A query styles descendants of the container, never the container itself. Put container-type on a wrapper (.card-slot) and style the component inside it.

Declare container-type on the parent

Without it, @container rules match nothing.

  • inline-size: queries on width; the usual choice.
  • size: queries on width and height; the container needs an explicit block size.
  • normal: not a size container.

A page-level container around the main column can drive nested components. Put container-type on a component wrapper rather than html or body: it applies layout containment, which makes the element the containing block for fixed and absolutely positioned descendants.

Name containers when nesting

An unnamed query matches the nearest ancestor container. Name nested containers so each rule targets the intended level; container: card / inline-size sets name and type together.

.cards-slot { container: cards / inline-size; }
.card-slot { container: card / inline-size; }
 
@container card (min-width: 24rem) { .card .title { font-size: 1.25rem; } }
@container cards (min-width: 60rem) { .cards { grid-template-columns: repeat(3, 1fr); } }

Size inside containers with cqi

cqi is 1% of the container’s inline size; cqb, cqw, cqh, cqmin, and cqmax cover the other axes.

.card .title { font-size: clamp(1rem, 4cqi, 1.5rem); }

Let components own their breakpoints

A reusable component declares its container and its queries; the page only places it. The same markup then stacks in a sidebar and spreads in a wide column. Use css-grid for the layout and tailwind-responsive for the @container utility variants.

Check support for newer query types

FeatureStatus (1 Oct 2026)
Size queriesWidely available
Style queries (@container style(...))Newly available (May 2026)
Name-only container queriesNewly available (May 2026)
Scroll-state queriesLimited availability

Ship size queries without fallbacks. Gate style and scroll-state queries behind @supports or feature checks.

Avoid common pitfalls

  • Missing container-type. The queries silently match nothing.
  • Wrong ancestor. Nested unnamed containers match the nearest; name them.
  • size without a block size. The container collapses; use inline-size unless you need height queries.
  • Reordering with grid-template-areas. Layout changes between queries can desync DOM and visual order; keep focus order sensible (accessibility).

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