<!DOCTYPE HTML>
<!--
     Any copyright is dedicated to the Public Domain.
     http://creativecommons.org/publicdomain/zero/1.0/
-->
<html><head>
  <title>Reference: 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">
  <style type="text/css">
html,body {
  color:black; background-color:white; font:16px/1 monospace; padding:0; margin:0;
}

.grid {
  display: inline-grid;
  position: relative;
  background: lightgrey;
  grid: 50px 50px / 50px 50px;
}

#item {
  background: grey;
  position: absolute;
  align-self: center;
  left: 20px;
}

  </style>
</head>
<body>

<div class="grid">
  <div id="item">X</div>
</div>

</body>
</html>