clip-path-on-fixed-position-scroll.html

<!DOCTYPE html>
<title>CSS Masking: Test out-of-view clip-path above fixed-position element scrolled into view</title>
<link rel="help" href="http://www.w3.org/TR/css-masking-1/#clipping-paths">
<link rel="help" href="https://www.w3.org/TR/css-position-3/#fixed-position">
<link rel="help" href="https://crbug.com/1400107">
<link rel="match" href="clip-path-on-fixed-position-scroll-ref.html">
<style>
div {
  width: 100px;
  height: 100px;
}
.clip {
  clip-path: inset(0);
}
.fixed {
  position: fixed;
  background: red;
  z-index: -1;
  bottom: 0;
}
.green {
  position: relative;
  background: green;
}
</style>
<div style="height: 800px">Scroll to the bottom. </div>
<div class="clip">
  <div class="fixed"></div>
  <div class="green"></div>
</div>
<script>
onload = () => {
  window.scrollTo(0, 400);
};
</script>

chromium/third_party/blink/web_tests/external/wpt/css/css-masking/clip-path/clip-path-on-fixed-position-scroll.html