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chromium/third_party/blink/web_tests/http/tests/inspector-protocol/resources/css-appearance-non-standard.html 

<!DOCTYPE html>

<button id=button>Test</button>
<script>
const [prop, value] = location.search.slice(1).split('&');
// Deprecation warning should be generated if a non standard appearance value was specified.
button.style = `${prop}: ${value}`;
</script>