css/css-contain/contain-paint-001.html

<!doctype html>
<html lang=en>
  <meta charset=utf-8>
  <title>CSS-contain test: paint containment use the padding edge</title>
  <link rel="author" title="Florian Rivoal" href="https://florian.rivoal.net">
  <meta name=flags content="">
  <meta name=assert content="paint containment clips at the padding edge, not content edge, and takes corner clipping into account">
  <link rel="match" href="reference/contain-paint-001-ref.html">
  <link rel=help href="https://drafts.csswg.org/css-contain-1/#containment-paint">

<style>
div {
  width: 100px;
  height: 100px;
  background: blue;
  padding: 50px;
  border-radius: 100px;
  contain: paint;
}
div::before {
 content:"";
 display: block;
 background: green;
 width: 100px;
 height: 100px;
}
div::after {
  content:"";
  display: block;
  background: red;
  width: 50px;
  height: 50px;
  margin-top: 38px;
  margin-left: -50px;
}
</style>

<p>Test passes if there is a green square in a rounded blue box, and no red.
<div></div>