chromium/third_party/blink/web_tests/external/wpt/css/css-anchor-position/idlharness.html

<!doctype html>
<title>CSS Anchor Positioning IDL tests</title>
<link rel="help" href="https://drafts.csswg.org/css-anchor-position-1/#interfaces">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/resources/WebIDLParser.js"></script>
<script src="/resources/idlharness.js"></script>

<style>
@position-fallback --fallback {
  @try {}
  @try {}
}
</style>

<script>
  'use strict';
  idl_test(
    ['css-anchor-position'],
    ['cssom'],
    idl_array => {
      try {
        self.positionFallback = document.styleSheets[0].cssRules.item(0);
        self.try1 = self.positionFallback.cssRules.item(0);
        self.try2 = self.positionFallback.cssRules.item(1);
      } catch (e) {
        // Will be surfaced when any rule is undefined below.
      }

      idl_array.add_objects({
        CSSPositionFallbackRule: ['positionFallback'],
        CSSTryRule: ['try1', 'try2'],
        CSSStyleDeclaration: ['try1.style', 'try2.style'],
      });
    }
  );
</script>