chromium/headless/test/data/centered_blue_box.html

<!doctype html>
<style>
body {
  overflow: hidden;
  min-width: 300px;
  min-height: 300px;
  background-image: linear-gradient(#0000ff, #0000ff);
  background-size: 100px auto;
  background-position: center;
  background-repeat: no-repeat;
}
</style>
<body>
</body>