<!DOCTYPE html>
<title>position:sticky elements should respect padding on their ancestor overflow element</title>
<link rel="help" href="https://www.w3.org/TR/css-position-3/#sticky-pos" />
<meta name="assert" content="This test checks that position:sticky elements respect padding on their ancestor overflow element" />

<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.scroller.style.padding = '20px 0';

  // Before sticking; the element isn't within the padding range.
  elements.scroller.scrollTop = 150;
  const nonStickyTopY = elements.container.offsetTop +
          elements.filler.clientHeight;
  assert_equals(elements.sticky.offsetTop, nonStickyTopY);
}, 'A sticky element should not be affected by ancestor padding until it ' +
    'reaches it');

test(() => {
  const elements = setupStickyTest('top', 50);
  elements.sticky.style.top = '0';
  elements.scroller.style.padding = '20px 0';

  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;
  const stickyOffset = targetTopY - nonStickyTopY;

  assert_equals(elements.sticky.offsetTop, nonStickyTopY + stickyOffset + 20);
}, 'A sticky element should be offset by ancestor padding even when stuck');

test(() => {
  const elements = setupStickyTest('top', 50);
  elements.sticky.style.top = '0';
  elements.scroller.style.padding = '20px 0';

  elements.scroller.scrollTop = 315;
  const maxOffsetInContainer = elements.container.offsetTop +
      elements.container.clientHeight - elements.sticky.clientHeight;
  assert_equals(elements.sticky.offsetTop, maxOffsetInContainer);
}, 'Ancestor overflow padding does not allow a sticky element to escape its ' +
    'container');
</script>
