Container queries begin to land in stable browsers while the polyfill gets a big update

# Container queries are here!

Exciting news—one of the most highly requested developer features has begun to land in web browsers! As of Chromium 105 and Safari 16, you can now create size-based container queries and use container query unit values in these browsers. To make it even easier to use size-based container queries and cq units, the Aurora team at Chrome has been hard at work updating the Container Query Polyfill to support more browsers and use cases so you can feel confident using this powerful feature today.

# What are container queries?

Container queries are a CSS feature which enables you to write styling logic that targets features of a parent element to style its children. You can create truly component-based responsive design by querying for a parent’s size. This is much more granular and useful information than something like media queries that only provide size information about the viewport.

With container queries, you can write reusable components that can appear differently based on where they live in the page. This makes them much more resilient and responsive across pages and templates.

# Using container queries

Say you have some HTML:

<!-- card parent -->
<div class=”card-parent”>
  <div class=”card>
     <!-- card contents -->
      …
  </div>
</div>

To use a container query, you first need to set containment on the parent element you want to track. Do this by setting the container-type property, or using the container shorthand to set the container type and container name at the same time.

.card-parent {
  /* query the inline-direction size of this parent */
  container-type: inline-size;
}

Now, you can use the @container rule to set styles based on the closest parent. For a design like the image above, where a card might go from one column to two columns, write something like:

@container (min-width: 300px) {
  .card {
    /* styles to apply when the card container (.card-parent in this case) is >= 300px */
    /* I.e. shift from 1-column to 2-column layout: */
    grid-template-columns: 1fr 1fr;
  }
}

To be more neat and explicit, give the parent element container a name:

.card-parent {
  container-type: inline-size;
  /* set name here, or write this in one line using the container shorthand */
  container-name: card-container;
}

Then rewrite the previous code as:

@container card-container (min-width: 300px) {
  .card {
    grid-template-columns: 1fr 1fr;
  }
}

# Container query units

To make container queries even more useful, you can use container-based unit values as well. The following table shows the possible container unit values and how they correspond to a container’s size:

One example for how you would use container-based units is responsive typography. The viewport-based units (such as vh, vb, vw, and vi) can be used to size any element on the screen.

.card h2 {
  font-size: 15cqi;
}

This code will make the font-size 15% of the inline size of the container, meaning it will get bigger as the inline size (width) increases, or smaller as it decreases. To take this even further, use the clamp() function to give your typography a minimum and maximum size limit, and size it responsively based on the container size:

.card h2 {
  font-size: clamp(1.5rem, 15cqi, 3rem);
}

Now the header will never get larger than 3rem or smaller than .5rem but it will take 15% of the container’s inline size anywhere in between.

This demo takes that a step further and updates the wider cards to have a smaller size range, as they present in a 2-column view.

# The container query polyfill

Because container queries are such a powerful feature, we want you to be able to feel comfortable incorporating it into your projects, and know that browser support is a big part of that. Because of this, we’ve been working on making improvements to the Container Query Polyfill. This polyfill has general support in:

• Firefox 69+
• Chrome 79+
• Edge 79+
• Safari 13.4+

It is under 9kb in size when compressed, and uses ResizeObserver with MutationObserver to support the full @container query syntax that is currently available in stable browsers:

• Discrete queries (width: 300px and min-width: 300px).
• Range queries (200px < width < 400px and width < 400px).
• Container relative length units (cqw, cqh, cqi, cqb, cqmin, and cqmax) in properties and keyframes.

# Using the container query polyfill

To use the polyfill, add this script tag to the head of your document: :

<script type="module">
  if (!("container" in document.documentElement.style)) {
    import("https://unpkg.com/container-query-polyfill@^0.2.0");
  }
</script>

You may also wish to use a service to conditionally deliver the polyfill based on User-Agent, or self-host it on your own origin.

For the best user experience, it's recommended that you initially only use the polyfill for content below-the-fold and use @supports queries to temporarily replace it with a loading indicator until the polyfill is ready to display it:

@supports not (container-type: inline-size) {
  .container,
  footer {
    display: none;
  }

  .loader {
    display: flex;
  }
}

On sufficiently fast networks and devices, or devices that natively support container queries, this loading indicator will never be displayed.

# New Polyfill Features

The updated polyfill supports:

• Nested @container rules.
• Nesting @container rules under @supports and @media queries and vice versa is supported.
• Conditional CSS such as @supports (container-type: inline-size) will pass after the polyfill loads.
• Full CSS syntax support (there is no longer any issue with putting comments anywhere that they are syntactically valid).
• Vertical writing modes (via writing-mode).
• Container Relative Units (cqw, cqh, etc) are supported within query conditions, property declarations, and animation keyframes. rem and em are supported in query conditions. Expanded container query syntax:
  • Range syntax (for example (200px < width < 400px)).
  • Equality queries (for example, (width = 200px)).
• Pseudo elements like ::before and ::after.
• Browsers without :is(...)/:where(...) are supported via an optional workaround
• The orientation and aspect-ratio feature queries.
• Correctly filtering queries based on features (for example, querying height on container: inline-size is correctly disallowed with a horizontal writing mode).
• DOM mutation (for example, <style> and <link> elements being removed at runtime).

# Polyfill limitations and warnings

If you are using the container query polyfill, there are a few missing features to watch out for:

• The Shadow DOM is not yet supported.
• Container Relative Units (for example, cqw and cqh) are not supported in @media query conditions.
  • Safari: Container Relative Units are not supported in animation keyframes prior to 15.4.
• calc(), min(), max(), or other mathematical functions are not yet supported in query conditions.
• This polyfill only works with inline and same-origin CSS. Cross origin stylesheets, and stylesheets in iframes (unless a polyfill is manually loaded) are not supported.
• layout and style containment requires underlying browser support:
  • Safari 15.4+
  • Firefox does not support style containment at this time, but is working on it.

# Warnings

• To prevent impacting FID and CLS, the polyfill makes no guarantees about when the first layout will occur, even if it’s loaded synchronously, except that it will attempt to avoid unreasonably delaying LCP. In other words, you should never rely on it for first paint.
• Generates ResizeObserver Loop Errors. The original polyfill does this too, but it’s worth calling out. This occurs because the block-size of a container-type: inline-size will likely change after evaluating a query, but ResizeObserver has no way to tell it that we don’t care about block-size changes.
• This polyfill is tested against Web Platform Tests and reached 70% passing since certain features like JavaScript APIs are not polyfilled, and so the pass rate is intentionally closer to 70%.
• The :where() workaround is required for the 2.23% users of browsers older than:
  • Safari 14
  • Chromium 88
    • Edge 88
    • Samsung Internet 15
  • Firefox 78