css/css-values/viewport-units-extreme-scale.html

<!DOCTYPE html>
<title>Scaling with viewport units</title>
<link rel="help" href="https://drafts.csswg.org/css-values-4/#viewport-relative-lengths">
<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1860338">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>

<iframe id=iframe width=640 height=480></iframe>

<script>

const doc = iframe.contentDocument;
const win = iframe.contentWindow;

function test_computed_value(value, expected) {
  test((t) => {
    t.add_cleanup(() => { doc.body.innerHTML = ''; });
    doc.body.innerHTML = `
      <!doctype html>
      <style>
        * { margin: 0; }
        body { height: 100%; }
        div { height: ${value}; }
      </style>
      <div></div>
    `;
    let div = doc.querySelector('div');
    assert_equals(win.getComputedStyle(div).height, expected);
  }, `${value} computes to ${expected}`);
}

// Check the basic units are as expected
test_computed_value('100vw', '640px');
test_computed_value('100vh', '480px');

// Try some calculations involving extreme scaling
test_computed_value('calc((1vw - 6.3999px) * 10000000)', '1000px');
test_computed_value('calc((100vh - 479px) * 60000)', '60000px');

</script>