chromium/third_party/blink/web_tests/wpt_internal/printing/page-fitting-002-print.html

<!DOCTYPE html>
<link rel="match" href="page-fitting-002-print-ref.html">
<script>
  if (window.testRunner) {
    testRunner.setPrintingSize(400, 300);
    testRunner.setPrintingMargin(20);
    // With a specified "paper size" above, fit each page to that. If the page
    // is smaller than the paper, center it on "paper". If it is larger than the
    // "paper", scale it down and center it on "paper". The orientation implied
    // by the page size descriptor should be honored.
    testRunner.setShouldCenterAndShrinkToFitPaper(true);
  }
</script>
<style>
  @page different {
    size: 375px 500px;
  }
  body {
    margin: 0;
    background: yellow;
  }
</style>
Default size.
<div style="page:different;">
  Scaled down, and in portrait mode.
</div>