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+<!DOCTYPE HTML>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html><head>
+  <title>CSS Flexbox Test: dynamic change .left on abs.pos. item w. align-self:center</title>
+  <link rel="author" title="Mats Palmgren" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1405319">
+  <link rel="help" href="https://drafts.csswg.org/css-align-3/#propdef-align-self">
+  <link rel="match" href="flexbox-item-align-self-dynamic-pos-001-ref.html">
+  <style type="text/css">
+html,body {
+  color:black; background-color:white; font:16px/1 monospace; padding:0; margin:0;
+}
+
+.flexbox {
+  display: flex;
+  position: relative;
+  height: 100px;
+}
+
+#item {
+  background: grey;
+  position: absolute;
+  align-self: center;
+  left: 10px;
+}
+
+</style>
+</head>
+<body>
+
+<div class="flexbox">
+  <div id="item">X</div>
+</div>
+
+<script>
+  document.body.offsetLeft;
+  var items = Array.prototype.slice.call(document.querySelectorAll('#item'));
+  items.map(item =>  item.style.left = "20px");
+  document.body.offsetLeft;
+</script>
+
+</body>
+</html>