mentById('test'));
  assert_equals(style.counterIncrement, 'foo 5');
}, 'basic sibling-count() test');

test(() => {
  let style = getComputedStyle(document.getElementById('test'));
  assert_equals(style.left, 'calc(10% + 200px)');
}, 'sibling-index() in calc() with percentage');

test(() => {
  let style = getComputedStyle(document.getElementById('test'), '::before');
  assert_equals(style.zIndex, '4');
  assert_equals(style.widows, '10');
}, 'sibling-count() on pseudo-element');

test(() => {
  let style 