transition-style-change-event-002.html

<!doctype html>
<meta charset="utf-8">
<title>Container Queries - Style Change Event for transitions</title>
<link rel="help" href="https://drafts.csswg.org/css-transitions/#starting">
<link rel="help" href="https://drafts.csswg.org/css-conditional-5/#animated-containers">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="support/cq-testcommon.js"></script>
<style>
  .container {
    container-type: inline-size;
  }
  #outer {
    width: 100px;
    color: green;
  }
  #target {
    transition: color 100s step-end;
  }

  @container (min-width: 200px) {
    #inner { color: red; }
  }
  @container (min-width: 200px) {
    #target {
      /* This rule exists just to have a container query dependency between
         target and #inner */
      background-color: orange;
    }
  }
</style>
<div id="outer" class="container">
  <div id="inner" class="container">
    <div id="target">Green</div>
  </div>
</div>
<script>
  setup(() => assert_implements_container_queries());

  test(() => {
    outer.offsetTop;
    outer.style.width = "200px";
    assert_equals(getComputedStyle(target).color, "rgb(0, 128, 0)");
  }, "#inner color change to red triggers a step transition starting at green");
</script>

chromium/third_party/blink/web_tests/external/wpt/css/css-conditional/container-queries/transition-style-change-event-002.html