mq-unknown-feature-custom-property.html

<!DOCTYPE html>
<title>Media Queries Test: Custom property name as media feature name</title>
<link rel="help" href="https://drafts.csswg.org/mediaqueries-4/#mq-syntax">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style id="media_sheet">
  @media (--FOO: bar) {}
</style>
<script>
  test(() => {
    assert_equals(media_sheet.sheet.cssRules[0].conditionText, "(--FOO: bar)")
  }, "Serialization of <mf-name> : <mf-value> with custom property feature name and ident value");
</script>

chromium/third_party/blink/web_tests/external/wpt/css/mediaqueries/mq-unknown-feature-custom-property.html