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<!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>
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