css/motion/offset-path-shape-shape-001.html

<!DOCTYPE html>
<meta charset="utf-8">
<title>CSS Motion Path test: &lt;basic-shape&gt; shape() function</title>
<link rel="help" href="https://drafts.fxtf.org/motion/#valdef-offset-path-basic-shape">
<link rel="help" href="https://drafts.csswg.org/css-shapes-2/#shape-function">
<link rel="match" href="offset-path-shape-shape-001-ref.html">
<meta name="assert" content="This tests that shape() generates a rotation and translation.">

<style>
#outer {
  top: 100px;
  left: 100px;
  position: relative;
  width: 600px;
  height: 400px;
}

#box {
  width: 100px;
  height: 100px;
  background-color: green;
  offset-path: shape(from 0px 0%,
                     hline by 100%,
                     vline to 400px,
                     hline by -100%,
                     close);
  offset-distance: 40%;
  border-radius: 50% 50% 0 0;
}
</style>

<div id="outer">
  <div id="box"></div>
</div>