css/css-values/viewport-units-writing-mode.html

<!DOCTYPE html>
<title>Viewport units are responsive to writing-mode changes</title>
<link rel="help" href="https://drafts.csswg.org/css-values-4/#viewport-relative-lengths">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>

<style>
  iframe {
    width: 200px;
    height: 100px;
  }
</style>

<iframe id=iframe></iframe>

<script>

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

function test_writing_mode(value, expected_pre, expected_post) {
  test((t) => {
    t.add_cleanup(() => { doc.body.innerHTML = ''; });
    doc.body.innerHTML = `
      <style>
        div {
          writing-mode: initial;
          height: ${value};
        }
        .vertical {
          writing-mode: vertical-rl;
        }
      </style>
      <div></div>
    `;
    let div = doc.querySelector('div');
    assert_equals(win.getComputedStyle(div).height, expected_pre);

    // The writing-mode of the document element does not matter.
    t.add_cleanup(() => { doc.documentElement.classList.remove('vertical'); })
    doc.documentElement.classList.add('vertical');
    assert_equals(win.getComputedStyle(div).height, expected_pre);

    // The writing-mode of the target element is what matters.
    div.classList.add('vertical');
    assert_equals(win.getComputedStyle(div).height, expected_post);
  }, `${value} computes to ${expected_post} with vertical writing-mode`);
}

test_writing_mode('100vi', '200px', '100px');
test_writing_mode('100svi', '200px', '100px');
test_writing_mode('100lvi', '200px', '100px');
test_writing_mode('100dvi', '200px', '100px');

test_writing_mode('100vb', '100px', '200px');
test_writing_mode('100svb', '100px', '200px');
test_writing_mode('100lvb', '100px', '200px');
test_writing_mode('100dvb', '100px', '200px');

</script>