<!DOCTYPE html>
<html lang="en">
<meta charset="utf-8">
<title>border-radius should work correctly for elements with preserve-3d</title>

<style>

#a {
  position: relative;
  width: 300px;
  height: 300px;
  border-radius: 10px;
  overflow: hidden;
  background: red;
}

#b {
  height: 100%;
  transform-style: preserve-3d;
  transform: rotateX(90deg);
}

#c {
  position: relative;
  background: green;
  height: 100%;
  width: 10000px;
  transform: rotateX(90deg);
}
</style>

<div id="a">
  <div id="b">
    <div id="c"></div>
  </div>
</div>