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<!DOCTYPE html>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<link rel="author" title="Emilio Cobos Álvarez" href="mailto:emilio@crisal.io">
<link rel="author" title="Mozilla" href="https://mozilla.org">
<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1543599">
<link rel="help" href="https://drafts.csswg.org/css-scroll-anchoring/#suppression-triggers">
<style>
#hidden {
display: none;
background: red;
}
#spacer {
height: calc(100vh + 200px); /* At least 200px of scroll range */
}
</style>
<table>
<thead>
<tr>
<th>1
<th>1
<th>1
<th>1
</tr>
</thead>
<thead id="hidden">
<tr>
<th>1
<th>1
<th>1
<th>1
</tr>
</thead>
<tbody>
<tr><td>0 <td>0 <td>0 <td>0 </tr>
<tr><td>0 <td>0 <td>0 <td>0 </tr>
<tr><td>0 <td>0 <td>0 <td>0 </tr>
<tr><td>0 <td>0 <td>0 <td>0 </tr>
<tr><td>0 <td>0 <td>0 <td>0 </tr>
<tr><td>0 <td>0 <td>0 <td>0 </tr>
<tr><td>0 <td>0 <td>0 <td>0 </tr>
</tbody>
</table>
<div id="spacer"></div>
<script>
let firstEvent = true;
const targetScrollPosition = 100;
const hidden = document.querySelector("#hidden");
const t = async_test("Scroll offset doesn't change when an element goes back and forth to display: none");
window.onscroll = t.step_func(function() {
hidden.style.display = "block";
hidden.style.position = "absolute";
hidden.style.visibility = "hidden";
window.unused = hidden.offsetHeight;
hidden.style.display = "";
hidden.style.position = "";
hidden.style.visibility = "";
if (firstEvent) {
firstEvent = false;
requestAnimationFrame(t.step_func(function() {
requestAnimationFrame(t.step_func_done(function() {
assert_equals(document.scrollingElement.scrollTop, targetScrollPosition);
}));
}));
}
});
window.onload = t.step_func(function() {
window.scrollTo(0, targetScrollPosition);
});
</script>
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