border-radius-on-squashed-layers.html

<!DOCTYPE html>
<style>
.precursor {
  width: 100px;
  height: 40px;
  background-color: blue;
  will-change: transform;
}
.container {
  position: relative;
  top: -45px;
  width: 100px;
  height: 40px;
  background-color: red;
  border: 1px solid black;
  border-radius: 10px;
  overflow: hidden;
}

.contents {
  background-color: green;
  height: 200px;
  width: 200px;
  position: relative;
  top: -10px;
  left: -10px;
}
</style>
<div class="precursor"></div>
<div class="container">
  <div class="contents"></div>
</div>

chromium/third_party/blink/web_tests/compositing/overflow/border-radius-on-squashed-layers.html