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chromium/third_party/blink/web_tests/external/wpt/css/css-color/light-dark-basic.html 

<!doctype html>
<title>light-dark() color-scheme propagation</title>
<script src=/resources/testharness.js></script>
<script src=/resources/testharnessreport.js></script>
<link rel="help" href="https://drafts.csswg.org/css-color-adjust/#color-scheme-effect">
<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/7561">
<div id="system"></div>
<div id="light" style="color-scheme: light"></div>
<div id="dark" style="color-scheme: dark"></div>
<script>
const system_is_dark = matchMedia("(prefers-color-scheme: dark)").matches;
const elements = ["system", "light", "dark"].map(document.getElementById.bind(document));
function test_light_dark(color, expected_light, expected_dark) {
  test(() => {
    for (let element of elements) {
      let should_be_dark = element.id == "dark" || (element.id == "system" && system_is_dark);
      element.style.backgroundColor = color;
      assert_not_equals(element.style.backgroundColor, "", "Should be valid");
      assert_equals(getComputedStyle(element).backgroundColor, should_be_dark ? expected_dark : expected_light);
    }
  }, color);
}

test_light_dark("light-dark(white, black)", "rgb(255, 255, 255)", "rgb(0, 0, 0)");
test_light_dark("light-dark(light-dark(white, red), red)", "rgb(255, 255, 255)", "rgb(255, 0, 0)");
</script>