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<!DOCTYPE html>
<title>CSS Positioned Layout Test: Auto margins resolve correctly after dynamic inset change</title>
<link rel="author" title="Ting-Yu Lin" href="tlin@mozilla.com">
<link rel="author" title="Mozilla" href="https://www.mozilla.org/">
<link rel="help" href="https://drafts.csswg.org/css-position-3/#abspos-margins">
<meta name="assert" content="Auto margins on abspos elements are resolved correctly after a dynamic change to inset.">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
#container {
position: relative;
width: 400px;
height: 400px;
}
#target-both {
position: absolute;
inset: 0;
margin: auto;
width: 200px;
height: 200px;
}
#target-inline {
position: absolute;
inset: 0;
margin: 0 auto;
width: 200px;
height: 200px;
}
</style>
<div id="container">
<div id="target-both"></div>
<div id="target-inline"></div>
</div>
<script>
// Force initial layout.
document.body.offsetTop;
test(() => {
document.getElementById("target-both").style.inset = "40px";
// Available margin space: 400 - 40 - 40 - 200 = 120px, so each auto margin = 60px.
// Expected offset from container edge: 40 + 60 = 100px.
assert_equals(document.getElementById("target-both").offsetLeft, 100,
"inline auto margin after inset change");
assert_equals(document.getElementById("target-both").offsetTop, 100,
"block auto margin after inset change");
}, "margin:auto on abspos resolves correctly after dynamic inset change");
test(() => {
document.getElementById("target-inline").style.inset = "40px";
// Inline axis: available margin space = 400 - 40 - 40 - 200 = 120px, each margin = 60px.
// Block axis: margin is 0, not auto.
assert_equals(document.getElementById("target-inline").offsetLeft, 100,
"inline auto margin after inset change");
assert_equals(document.getElementById("target-inline").offsetTop, 40,
"zero block margin after inset change");
}, "margin:0 auto on abspos resolves correctly after dynamic inset change");
</script>
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