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chromium/third_party/blink/web_tests/external/wpt/css/cssom-view/screenLeftTop.html 

<!DOCTYPE html>
<link rel="help" href="https://drafts.csswg.org/cssom-view/#dom-window-screenleft">
<link rel="help" href="https://drafts.csswg.org/cssom-view/#dom-window-screentop">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script>
test(() => {
  assert_equals(typeof window.screenLeft, "number", "screenLeft type");
  assert_equals(window.screenLeft, window.screenX, "alias of screenX");
}, "screenLeft");

test(() => {
  assert_equals(typeof window.screenTop, "number", "screenTop type");
  assert_equals(window.screenTop, window.screenY, "alias of screenY");
}, "screenTop");
</script>