This is a testharness.js-based test.
[PASS] Custom properties are not allowed in @font-face rules
[FAIL] Custom properties are not allowed in the outer scope of @keyframes rules
  assert_equals: expected "@keyframes foo {\n  0% { --valid-var: 4; }\n  100% { left: 10px; }\n}" but got "@keyframes foo { \n  100% { left: 10px; }\n}"
Harness: the test ran to completion.