css/selectors/is-where-shadow.html

<!DOCTYPE html>
<title>:is() inside shadow pseudos</title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<link rel="help" href="https://drafts.csswg.org/selectors-4/#matches">
<link rel="help" href="https://drafts.csswg.org/css-scoping/#host-selector">
<link rel="help" href="https://drafts.csswg.org/css-scoping/#slotted-pseudo">
<div class="parent1"><div id="host1" class=a><p class=e>::slotted</p></div></div>
<div class="parent2"><div id="host2" class=b><p class=d>::slotted</p></div></div>
<div class="parent3"><div id="host3" class=c><p class=f>::slotted</p></div></div>
</div>
<script>
  let shadow1 = host1.attachShadow({ mode: 'open' });
  let shadow2 = host2.attachShadow({ mode: 'open' });
  let shadow3 = host3.attachShadow({ mode: 'open' });

  const html = `
    <style>
      * { color: blue; }
      :host(:is(.a, .b)) b { color: green; }
      :host-context(:is(.parent1, .parent2)) i { color: green; }
      ::slotted(:is(.e, .f)) { color: green; }

      /* The following should not match: */
      :host(:is(.z)) b { color: red; }
      :host(:is(.a + .b)) b { color: red; }
      :host-context(:is(.z)) i { color: red; }
      :host-context(:is(.parent1 .parent2)) i { color: red; }
      ::slotted(:is(.z)) { color: red; }
      ::slotted(:is(.a > .b)) { color: red; }
    </style>
    <b>:host</b>
    <i>:host-context</i>
    <slot></slot>
  `;

  shadow1.innerHTML = html;
  shadow2.innerHTML = html;
  shadow3.innerHTML = html;

  const getComputedColor = e => getComputedStyle(e).color;
  const green = 'rgb(0, 128, 0)';
  const blue = 'rgb(0, 0, 255)';

  test(function() {
    assert_equals(getComputedColor(shadow1.querySelector('b')), green);
    assert_equals(getComputedColor(shadow2.querySelector('b')), green);
    assert_equals(getComputedColor(shadow3.querySelector('b')), blue);
  }, ':is() inside :host()');

  test(function() {
    assert_equals(getComputedColor(shadow1.querySelector('i')), green);
    assert_equals(getComputedColor(shadow2.querySelector('i')), green);
    assert_equals(getComputedColor(shadow3.querySelector('i')), blue);
  }, ':is() inside :host-context()');

  test(function() {
    assert_equals(getComputedColor(document.querySelector('.e')), green);
    assert_equals(getComputedColor(document.querySelector('.d')), blue);
    assert_equals(getComputedColor(document.querySelector('.f')), green);
  }, ':is() inside ::slotted()');
</script>