<!DOCTYPE html>
<title>Tests CSS transition of anchor() across three 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;
}

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

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

<script>
setup(() => {
let shadow = host.attachShadow({mode: 'open'});
shadow.innerHTML = `
  <style>
    div {
      width: 100px;
      height: 100px;
      background: orange;
    }
    #anchor2 {
      margin-left: 200px;
      anchor-name: --a;
    }
    #anchor3 {
      margin-left: 400px;
    }
    #target {
      position: fixed;
      background: lime;
      top: 300px;
      transition: left 10s -5s linear;
    }
    #target.after {
      left: anchor(--a left);
    }
  </style>
  <div id="anchor2"></div>
  <div id="anchor3">
    <div id="target" part="target"></div>
  </div>
`;

let anchor3 = shadow.getElementById('anchor3');
let innerShadow = anchor3.attachShadow({mode: 'open'});
innerShadow.innerHTML = `
  <style>
    :host { anchor-name: --a; }
    ::slotted(*) { left: anchor(--a left); }
  </style>
  <slot></slot>
`;
});

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

  // Forces layout
  target.offsetLeft;

  // Triggers a transition from using #anchor3 to using #anchor2,
  // starting immediately at 50% progress
  target.classList.add('after');
  assert_equals(target.offsetLeft, 300);

  // Triggers another transition to using #anchor1 while the previous
  // transition is still in progress.
  host.classList.add('after');
  assert_equals(target.offsetLeft, 150);
}, 'Transition with anchor names defined in three different tree scopes');
</script>
