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Correctly propagate scroll margin for ancestor scroll into view #57422

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Jan 29, 2026
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Correctly propagate scroll margin for ancestor scroll into view #57422

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314 changes: 314 additions & 0 deletions css/css-scroll-snap/scroll-margin-overflow-ancestor.html
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<!DOCTYPE html>
<link rel="help" href="https://drafts.csswg.org/css-scroll-snap-1/#scroll-margin" />
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
.scroller {
overflow: auto;
position: relative;
height: 200px;
width: 100px;
border: 1px solid black;
}
/* Create scrollable content. */
.scroller::after {
content: "";
display: block;
height: 2000px;
}
/* Outer scroller container is positioned at 1000px */
.tests > .scroller > * {
position: relative;
top: 999px; /* content inside container starts at 1000px */
height: 150px;
width: 90%;
margin: 0 auto;
border: 1px solid black;
}
.visible {
overflow: visible;
}
.clip {
overflow: clip;
}
.target {
background: green;
height: 40px;
width: 40px;
margin: 0 auto;
position: relative;
}
.scroll-margin {
scroll-margin-top: 40px;
}
.scroll-padding {
scroll-padding-top: 20px;
}
.slightly-down { top: 20px; }
.far-down { top: 400px; }
.slightly-up { top: -20px; }
.tests {
display: flex;
}
</style>
<h3>overflow: visible</h3>
<div id="overflow-visible" class="tests">
<div class="scroller">
<div class="visible">
<div class="scroll-margin target far-down"></div>
</div>
</div>
<div class="scroller">
<div class="visible">
<div class="scroll-margin target slightly-down"></div>
</div>
</div>
<div class="scroller">
<div class="visible">
<div class="scroll-margin target at-top"></div>
</div>
</div>
<div class="scroller">
<div class="visible">
<div class="scroll-margin target slightly-up"></div>
</div>
</div>
</div>

<h3>overflow: clip</h3>
<div id="overflow-clip" class="tests">
<div class="scroller">
<div class="clip">
<div class="scroll-margin target far-down"></div>
</div>
</div>
<div class="scroller">
<div class="clip">
<div class="scroll-margin target slightly-down"></div>
</div>
</div>
<div class="scroller">
<div class="clip">
<div class="scroll-margin target at-top"></div>
</div>
</div>
<div class="scroller">
<div class="clip">
<div class="scroll-margin target slightly-up"></div>
</div>
</div>
</div>

<h3>overflow: auto</h3>
<div id="overflow-auto" class="tests">
<div class="scroller">
<div class="scroller">
<div class="scroll-margin target far-down"></div>
</div>
</div>
<div class="scroller">
<div class="scroller">
<div class="scroll-margin target slightly-down"></div>
</div>
</div>
<div class="scroller">
<div class="scroller">
<div class="scroll-margin target at-top"></div>
</div>
</div>
<div class="scroller">
<div class="scroller">
<div class="scroll-margin target slightly-up"></div>
</div>
</div>
</div>

<h3>overflow: auto with scroll padding</h3>
<div id="overflow-auto-scroll-padding" class="tests">
<div class="scroller scroll-padding">
<div class="scroller scroll-padding">
<div class="scroll-margin target far-down"></div>
</div>
</div>
<div class="scroller scroll-padding">
<div class="scroller scroll-padding">
<div class="scroll-margin target slightly-down"></div>
</div>
</div>
<div class="scroller scroll-padding">
<div class="scroller scroll-padding">
<div class="scroll-margin target at-top"></div>
</div>
</div>
<div class="scroller scroll-padding">
<div class="scroller scroll-padding">
<div class="scroll-margin target slightly-up"></div>
</div>
</div>
</div>

<script>
// Scroll all target elements into view.
for (const target of document.querySelectorAll('.target')) {
target.scrollIntoView();
}
// Scroll main frame to top
document.scrollingElement.scrollTo(0, 0);

test(() => {
const container = document.getElementById('overflow-visible');

// The element is 400px below container at 1400px,
// we should scroll to 1360 to give a 40px scroll margin.
const farDownScroller = container.querySelector('.scroller:has(.far-down)');
assert_equals(farDownScroller.scrollTop, 1360,
'gives 40px margin to element far below visible container');

// The element is 20px below container at 1020px,
// we should scroll to 980 to give a 40px scroll margin.
const slightlyDownScroller = container.querySelector('.scroller:has(.slightly-down)');
assert_equals(slightlyDownScroller.scrollTop, 980,
'gives 40px margin to element slightly below visible container');

// The element is at top of container at 1000px,
// we should scroll to 960 to give a 40px scroll margin.
const atTopScroller = container.querySelector('.scroller:has(.at-top)');
assert_equals(atTopScroller.scrollTop, 960,
'gives 40px margin to element at top of visible container');

// The element is 20px above container at 980px,
// we should scroll to 940 to give a 40px scroll margin.
const aboveTopScroller = container.querySelector('.scroller:has(.slightly-up)');
assert_equals(aboveTopScroller.scrollTop, 940,
'gives 40px margin to element slightly above visible container');

}, "scroll-margin is respected when overflowing an overflow: visible container");

test(() => {
const container = document.getElementById('overflow-clip');

// The element is 400px below container at 1400px,
// we should scroll to 1360 to give a 40px scroll margin
// even though the element is completely clipped.
const farDownScroller = container.querySelector('.scroller:has(.far-down)');
assert_equals(farDownScroller.scrollTop, 1360,
'gives 40px margin to element far below clip container');

// The element is 20px below container at 1020px,
// we should scroll to 980 to give a 40px scroll margin.
const slightlyDownScroller = container.querySelector('.scroller:has(.slightly-down)');
assert_equals(slightlyDownScroller.scrollTop, 980,
'gives 40px margin to element slightly below clip container');

// The element is at top of container at 1000px,
// we should scroll to 960 to give a 40px scroll margin.
const atTopScroller = container.querySelector('.scroller:has(.at-top)');
assert_equals(atTopScroller.scrollTop, 960,
'gives 40px margin to element at top of clip container');

// The element is 20px above container at 980px,
// we should scroll to 940 to give a 40px scroll margin
// even though the top of the element is clipped.
const aboveTopScroller = container.querySelector('.scroller:has(.slightly-up)');
assert_equals(aboveTopScroller.scrollTop, 940,
'gives 40px margin to element slightly above clip container');

}, "scroll-margin is respected when overflowing an overflow: clip container");

test(() => {
const container = document.getElementById('overflow-auto');

// The element is 400px below container at 1400px,
// we should scroll inner container to 360 to give 40px margin,
// and scroll outer container to 1000px to bring it to the top.
const farDownScroller = container.querySelector('.scroller:has(.far-down)');
const farDownInnerScroller = farDownScroller.querySelector('.scroller');
assert_equals(farDownInnerScroller.scrollTop, 360,
'gives 40px margin to element far down in inner scroller');
assert_equals(farDownScroller.scrollTop, 1000,
'scrolls to top of outer scroller');

// The element is 20px below container at 1020px,
// we can only give it 20px of margin in the inner scroller by scrolling to 0,
// so we should give it an additional 20px of margin in the outer scroller.
const slightlyDownScroller = container.querySelector('.scroller:has(.slightly-down)');
const slightlyDownInnerScroller = slightlyDownScroller.querySelector('.scroller');
assert_equals(slightlyDownInnerScroller.scrollTop, 0,
'gives all 20px possible for 40px margin in inner scroller');
assert_equals(slightlyDownScroller.scrollTop, 980,
'gives remaining 20px margin on outer scroller');

// The element is at top of container at 1000px,
// we can't give any margin on the inner scroller,
// we should scroll to 960 to give a 40px scroll margin.
const atTopScroller = container.querySelector('.scroller:has(.at-top)');
const atTopInnerScroller = atTopScroller.querySelector('.scroller');
assert_equals(atTopInnerScroller.scrollTop, 0,
'scrolls to top of inner scroller');
assert_equals(atTopScroller.scrollTop, 960,
'gives 40px margin to element in outer scroller');

// The element is 20px above container at 980px,
// we should scroll the inner container to the top,
// and since the element is above we still
// only need to give 40px above the inner scroller of margin.
const aboveTopScroller = container.querySelector('.scroller:has(.slightly-up)');
const aboveTopInnerScroller = aboveTopScroller.querySelector('.scroller');
assert_equals(aboveTopInnerScroller.scrollTop, 0,
'scrolls to top of inner scroller');
assert_equals(aboveTopScroller.scrollTop, 960,
'gives 40px margin to element slightly above inner scroller');

}, "scroll-margin is respected when overflowing an overflow: auto container");

test(() => {
const container = document.getElementById('overflow-auto-scroll-padding');

// The element is 400px below container at 1400px,
// we should scroll inner container to 340 to give 40px margin + 20px padding,
// and scroll outer container to 1000px as this will also have
// 40px margin + 20px padding from the target box.
const farDownScroller = container.querySelector('.scroller:has(.far-down)');
const farDownInnerScroller = farDownScroller.querySelector('.scroller');
assert_equals(farDownInnerScroller.scrollTop, 340,
'gives 40px margin and 20px padding to element far down in inner scroller');
assert_equals(farDownScroller.scrollTop, 1000,
'scrolls to top of outer scroller');

// The element is 20px below container at 1020px,
// we can only give it 20px of margin in the inner scroller by scrolling to 0,
// so we should give it an additional 20px of margin and 20px padding
// in the outer scroller plus an additional 20px padding for the outer
// scroller's padding. Note we don't duplicate the padding the inner
// scroller has already reserved.
const slightlyDownScroller = container.querySelector('.scroller:has(.slightly-down)');
const slightlyDownInnerScroller = slightlyDownScroller.querySelector('.scroller');
assert_equals(slightlyDownInnerScroller.scrollTop, 0,
'gives all 20px possible in inner scroller');
assert_equals(slightlyDownScroller.scrollTop, 960,
'gives remaining 20px margin and 20px padding on outer scroller');

// The element is at top of container at 1000px,
// we can't give any margin or padding on the inner scroller,
// we should scroll to 940 to give a 40px scroll margin + 20px padding.
const atTopScroller = container.querySelector('.scroller:has(.at-top)');
const atTopInnerScroller = atTopScroller.querySelector('.scroller');
assert_equals(atTopInnerScroller.scrollTop, 0,
'scrolls to top of inner scroller');
assert_equals(atTopScroller.scrollTop, 940,
'gives 40px margin and 20px padding to element in outer scroller');

// The element is 20px above container at 980px,
// we should scroll the inner container to the top,
// and since the element is above we still
// only need to give 40px margin + 20px padding above the inner scroller of margin.
const aboveTopScroller = container.querySelector('.scroller:has(.slightly-up)');
const aboveTopInnerScroller = aboveTopScroller.querySelector('.scroller');
assert_equals(aboveTopInnerScroller.scrollTop, 0,
'scrolls to top of inner scroller');
assert_equals(aboveTopScroller.scrollTop, 940,
'gives 40px margin and 20px padding to element slightly above inner scroller');

}, "scroll-margin and scroll-padding are respected when overflowing an overflow: auto container");

</script>