css/css-variables/revert-in-fallback.html

<!DOCTYPE html>
<title>CSS Custom Properties: Using revert in fallbacks</title>
<link rel="help" href="https://drafts.csswg.org/css-variables/#substitute-a-var">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
  body.revert {
    --x:FAIL;
    margin: -1px;
    display: grid;

    --x: var(--unknown, revert);
    margin: var(--unknown, revert);
    display: var(--unknown, revert);
  }
</style>
<html>
  <body>
    <pre id=out></pre>
    <script>
      let body_ua_display = getComputedStyle(document.body).display;
      let body_ua_margin = getComputedStyle(document.body).margin;
      document.body.classList.add('revert');

      test((t) => {
        assert_equals(getComputedStyle(document.body).getPropertyValue('--x'), '');
      }, 'var(--unknown, revert) in custom property');

      test((t) => {
        assert_equals(getComputedStyle(document.body).getPropertyValue('margin'), body_ua_margin);
      }, 'var(--unknown, revert) in shorthand');

      test((x) => {
        assert_equals(getComputedStyle(document.body).getPropertyValue('margin-left'), body_ua_margin);
      }, 'var(--unknown, revert) in shorthand observed via longhand');

      test((t) => {
        assert_equals(getComputedStyle(document.body).getPropertyValue('display'), body_ua_display);
      }, 'var(--unknown, revert) in longhand');
    </script>
  </body>
</html>