css/css-masking/hit-test/clip-path-shape-polygon-and-box-shadow.html

<!DOCTYPE html>
<title>Hit-test of clip-path polygon combined with box-shadow</title>
<link rel="help" href="https://drafts.fxtf.org/css-masking/#the-clip-path">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
body {
  margin: 0;
}
.box {
  width: 100px;
  height: 100px;
  background-color: blue;
  box-shadow: -100px 0px red;
  clip-path: polygon(50% 0, 100% 50%, 50% 100%, 0 50%);
}
</style>
<div class="box"></div>
<script>
function assert_element_at(element, pointlist) {
  for (let point of pointlist) {
    let result = document.elementFromPoint(point[0], point[1]);
    assert_equals(result, element, point.join(','));
  }
}

test(function() {
  let div = document.querySelector('.box');

  // Points inside clip-path.
  assert_element_at(div, [[50, 50], [50, 25], [50, 75], [25, 50], [75, 50]]);

  // Points outside clip-path.
  assert_element_at(document.body, [[20, 20], [80, 20], [20, 80], [80, 80]]);
});
</script>