tests/wpt/mozilla/tests/css/inline_block_centering_ref.html

<!DOCTYPE html>
<meta charset="utf-8">
<!--
    Tests that the popular inline-block centering technique works.

    See: https://s.codepen.io/shshaw/fullpage/gEiDt?#Inline-Block
-->
<style>
div {
    position: absolute;
    width: 100px;
    left: 0;
}
#a {
    background: blue;
    height: 100px;
    top: 0;
}
#b {
    background: green;
    height: 50px;
    top: 25px;
}
</style>
<div id=a><div id=b>