css/css-values/attr-container-style-query.html

<!DOCTYPE html>
<title>CSS Values and Units Test: attr() in container style queries</title>
<link rel="help" href="https://drafts.csswg.org/css-conditional-5/#container-queries">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
  #container {
    --foo: bar;
  }
  @container style(--foo: attr(data-foo type(<custom-ident>))) {
    #target { color: green; }
  }
</style>
<div id="container" data-foo="bar">
  <div id="target">Should be green</div>
</div>
<script>
  test(() => {
    assert_equals(getComputedStyle(target).color, "rgb(0, 128, 0)");
  }, "style query should implement to true");
</script>