<!DOCTYPE html>
<title>Tests CSS transition of anchor() across tree scopes</title>
<link rel="help" href="https://drafts4.csswg.org/css-anchor-position-1/">
<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/8180"></script>
<link rel="author" href="mailto:xiaochengh@chromium.org">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>

<style>
body {
  margin: 0;
}

#anchor1 {
  width: 100px;
  height: 100px;
  background: orange;
  anchor-name: --a;
}

#anchor2 {
  width: 100px;
  height: 100px;
  margin-top: 200px;
  margin-left: 300px;
  background: orange;
}

#anchor2.after::part(target) {
  top: anchor(--a top);
  left: anchor(--a right);
}
</style>

<div id="anchor1"></div>
<div id="anchor2"></div>

<script>
setup(() => {
  let shadow = anchor2.attachShadow({mode: 'open'});
  shadow.innerHTML = `
    <style>
      :host { anchor-name: --a; }
      #target {
        position: fixed;
        width: 100px;
        height: 100px;
        background: lime;
        top: anchor(--a top);
        left: anchor(--a right);
        transition: all 10s -5s linear;
      }
    </style>
    <div id="target" part="target"></div>
  `;
});

test(() => {
  let target = anchor2.shadowRoot.getElementById('target');

  // Forces layout
  target.offsetLeft;

  // Triggers a transition from using #anchor2 to using #anchor1,
  // starting immediately at 50% progress.
  anchor2.classList.add('after');
  assert_equals(target.offsetLeft, 250);
  assert_equals(target.offsetTop, 150);
}, 'Transition with anchor names defined in different tree scopes');
</script>
