0.1.2 • Public • Published

    Container Query Polyfill

    A tiny polyfill for CSS Container Queries, weighing about 1.6kB brotli’d. It transpiles CSS code on the client-side and implements Container Query functionality using ResizeObserver and MutationObserver.


    Ideally, the polyfill is only loaded if the browser doesn’t support Container Queries natively. In a modern setup with a bundler that uses ES modules, the following snippet should work:

    const supportsContainerQueries = "container" in;
    if (!supportsContainerQueries) {

    If you are in a legacy setup (or just want to prototype quickly), there’s also an IIFE version that you can include using a <script> tag:

    <script src=""></script>

    Browser support

    The polyfill relies on ResizeObserver, MutationObserver and :is(). Therefore, it should work in all modern browsers, specifically Chrome/Edge 88+, Firefox 78+ and Safari 14+.

    Feature support & limitations

    My aim is to make the polyfill work correctly for the majority of use-cases, but cut corners where possible to keep the polyfill simple(-ish), small and efficient. The limitations arising from these tradeoffs are listed below.

    (These decisions can be revisited if they pose a significant hurdle and there is a good way to implement them. Please open an issue!)

    • Both the old CQ syntax as well as the new syntax are supported:
    /* These are all equivalent */
    @container (min-width: 200px) {
      /* ... */
    @container (width >= 200px) {
      /* ... */
    @container size(width >= 200px) {
      /* ... */
    • Boolean operations (and, or and not) are supported.
    • The polyfill does not support style queries (e.g. @container style(--color: red)), as there is no way to get notified of computed style changes.
    • The polyfill does not support pseudo elements (::before & ::after), as they don’t have a real DOM handle and can't be observed with ResizeObserver.
    • Container Queries will not work when nested inside a Media Query. For now, the polyfill only supports top-level CQs.
    • Container Query thresholds can only be specified using pixels.
    • Due to the nature of CORS, the polyfill only attempts to handle same-origin and inline stylesheets. Cross-origin stylesheets are not processed, regardless of CORS headers.
    • CQs inside ShadowDOM are not supported yet.
    • Don’t do weird interspersed comments, okay? Like @container /* here’s a comment! */ (min-width: 1px) { ... }. Just don’t.

    Building & Testing

    This project uses esbuild to bundle the project, which is automatically installed via npm. To build the polyfill, run:

    npm run build

    To run the tests, run

    npm run serve

    and open your browser at

    License Apache-2.0




    npm i container-query-polyfill

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    67.2 kB

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    • developit
    • una
    • surma