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

<!doctype html>
<meta charset="utf-8">
<title>CSS Motion Path test: &lt;basic-shape&gt; circle() path with explicit arguments</title>
<meta name="fuzzy" content="maxDifference=0-150; totalPixels=0-300">
<link rel="author" title="Daniil Sakhapov" href="sakhapov@google.com">
<link rel="match" href="offset-path-shape-circle-001-ref.html">
<link rel="help" href="https://drafts.fxtf.org/motion/#valdef-offset-path-basic-shape">

<style>
#outer {
  top: 100px;
  left: 100px;
  position: relative;
  width: 600px;
  height: 400px;
}
#box {
  background-color: green;
  position: relative;
  offset-path: circle(closest-side at center);
  offset-distance: 25%;
  border-radius: 50% 50% 0 0;
  width: 100px;
  height: 100px;
}
</style>

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