css/css-values/if-supports-quirks.html

<!-- quirks mode -->
<title>CSS Values and Units Test: CSS inline if() function supports() in quirks mode</title>
<meta name="assert" content="Test inline if() function with supports() query in quirks mode">
<link rel="help" href="https://drafts.csswg.org/css-values-5/#if-notation">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
    div {
      color: red;
      --x: if(supports(width: 30): true_value; else: false_value;)
    }
</style>
<div id="if">test</div>
<script>
  setup({ single_test: true });
  var elem = document.getElementById("if");
  let val = window.getComputedStyle(elem).getPropertyValue("--x");
  assert_equals(val, "true_value");
  done();
</script>