<!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-contain-3/#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: size }
  #outer {
    width: 100px;
    color: green;
  }
  @container (min-width: 200px) {
    #inner { color: red }
  }
  @container (min-width: 400px) {
    #target {
      color: green;
      transition: color 1s step-start;
    }
  }
</style>
<div id="outer" class="container">
  <div id="inner" class="container">
    <div id="target">Green</div>
  </div>
</div>
</div>
<script>
  setup(() => assert_implements_container_queries());

  const t = async_test("");
  const event_handler = t.step_func_done((e) => {
    assert_unreached("Transition event incorrectly triggered: " + e.type);
  });
  for (let event_name of ["transitionrun",
                          "transitionstart",
                          "transitionend",
                          "transitioncancel"]) {
    target.addEventListener(event_name, event_handler);
  }

  outer.offsetTop;
  // #target is green. Making the #outer container 200px will turn #inner and
  // #target red through inheritance.
  outer.style.width = "200px";
  // Making #inner 400px will make #target green.
  inner.style.width = "400px";
  // Both changes above should happen in one style change event and should not
  // trigger any transition events. Run two rAFs to make sure any events have
  // time to trigger.
  requestAnimationFrame(() => requestAnimationFrame(t.step_func_done(() => {
    assert_equals(getComputedStyle(inner).color, "rgb(255, 0, 0)",
        "@container queries supported");
  })));
</script>
