<!DOCTYPE html>
<title>position:sticky elements should properly interact with margins</title>
<link rel="help" href="https://www.w3.org/TR/css-position-3/#sticky-pos" />
<meta name="assert" content="position:sticky elements should ignore margins when sticking, but consider them when making sure sticky elements do not escape their containing block" />

<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>

<script src="resources/sticky-util.js"></script>

<body></body>

<script>
test(() => {
    const elements = setupStickyTest('top', 50);
    elements.sticky.style.margin = '15px';
    elements.scroller.scrollTop = 100;
    assert_equals(elements.sticky.offsetTop,
        elements.container.offsetTop + elements.filler.clientHeight + 15);
}, 'Before sticking, the margin should be obeyed.');

test(() => {
  const elements = setupStickyTest('top', 50);
  elements.sticky.style.margin = '15px';

  elements.scroller.scrollTop = 200;

  // This math cancels to sticky.offsetTop == (scroller.scrollTop + 50), but
  // for clarity the calculations are left explicit.
  const nonStickyTopY = elements.container.offsetTop +
    elements.filler.clientHeight;
  const targetTopY = elements.scroller.scrollTop + 50;
  const stickyOffset = targetTopY - nonStickyTopY;

  assert_equals(elements.sticky.offsetTop, nonStickyTopY + stickyOffset);
}, 'Whilst stuck, the margin is irrelevant.');

test(() => {
  const elements = setupStickyTest('top', 50);
  elements.sticky.style.margin = '15px';

  elements.scroller.scrollTop = 300;

  const maxOffsetInContainer = elements.container.offsetTop +
    elements.container.clientHeight - elements.sticky.clientHeight;
  assert_equals(elements.sticky.offsetTop, maxOffsetInContainer - 15);
}, 'The margin is taken into account when making sure the sticky element ' +
    'does not escape its container');
</script>