<!DOCTYPE html>
<title>@container-dependent elements respond to size changes of an @container-dependent iframe</title>
<link rel="help" href="https://drafts.csswg.org/css-contain-3/#size-container">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="support/cq-testcommon.js"></script>
<style>
  #container {
    container-type: size;
    width: 200px;
    height: 200px;
  }
  iframe {
    width: 200px;
    height: 40px;
  }
  @container (width > 300px) {
    iframe { width: 400px; }
  }
</style>
<div id=container>
  <iframe id=iframe srcdoc="
    <style>
      div#container {
        container-type: size;
        height: 20px;
      }
      div#child { color: red; }
      @container (width > 300px) {
        div#child { color: green; }
      }
    </style>
    <div id=container>
      <div id=child>Test</div>
    </div>
  "></iframe>
</div>
<script>
  setup(() => assert_implements_container_queries());

  function waitForLoad(w) {
    return new Promise(resolve => w.addEventListener('load', resolve));
  }

  promise_test(async () => {
    await waitForLoad(window);
    let inner_div = iframe.contentDocument.querySelector('div#child');
    assert_equals(getComputedStyle(inner_div).color, 'rgb(255, 0, 0)');

    // Changing the size of the outer container changes the size of the iframe,
    // which in turn should change the size of the inner container (inside that
    // iframe).
    container.style.width = '400px';
    container.style.setProperty('--x', 'x'); // crbug.com/1312940

    assert_equals(getComputedStyle(inner_div).color, 'rgb(0, 128, 0)');
  });
</script>
