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<!DOCTYPE html>
<title>Tests that position fallback responds to scrolling</title>
<link rel="author" href="mailto:xiaochengh@chromium.org">
<link rel="help" href="https://drafts.csswg.org/css-anchor-1/#scroll">
<link rel="help" href="https://drafts.csswg.org/css-anchor-1/#fallback-apply">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="support/test-common.js"></script>
<style>
#cb {
width: 400px;
height: 400px;
margin: 100px;
transform: scale(1);
outline: 1px solid black;
}
#scroller {
width: 400px;
height: 400px;
overflow: scroll;
}
#anchor {
width: 100px;
height: 100px;
margin-left: 150px;
margin-right: 275px;
margin-top: 300px;
margin-bottom: 300px;
background: orange;
anchor-name: --a;
}
#anchored {
position: absolute;
background: green;
position-anchor: --a;
position-try-options: --f1, --f2;
width: 100px; height: 100px;
/* Above the anchor */
left: anchor(left);
bottom: anchor(top);
}
@position-try --f1 {
/* Left of the anchor */
right: anchor(left);
top: anchor(top);
bottom: auto;
left: auto;
}
@position-try --f2 {
/* Right of the anchor */
left: anchor(right);
top: anchor(top);
bottom: auto;
}
</style>
<div id="cb">
<div id="scroller">
<div id="anchor"></div>
</div>
<div id="anchored"></div>
</div>
<script>
promise_test(async () => {
await waitUntilNextAnimationFrame();
assert_fallback_position(anchored, anchor, 'top');
}, 'Should be above the anchor when at initial scroll position');
promise_test(async () => {
scroller.scrollTop = 200;
await waitUntilNextAnimationFrame();
assert_fallback_position(anchored, anchor, 'top');
}, 'Scroll down until the top edge of #anchor touches container but not overflowing');
promise_test(async () => {
scroller.scrollTop = 201;
await waitUntilNextAnimationFrame();
assert_fallback_position(anchored, anchor, 'left');
}, 'Scroll further down, making the first fallback position overflow by 1px');
promise_test(async () => {
scroller.scrollTop = 200;
await waitUntilNextAnimationFrame();
assert_fallback_position(anchored, anchor, 'top');
}, 'Scroll back up to reuse the first fallback position');
promise_test(async () => {
scroller.scrollTop = 249;
scroller.scrollLeft = 51;
await waitUntilNextAnimationFrame();
assert_fallback_position(anchored, anchor, 'right');
}, 'Scroll bottom-right to make the first three fallback positions overflow');
</script>
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