<!DOCTYPE html>
<html>
<head>
  <title>background-position: left bottom 50%</title>
  <style type="text/css">
#outer
{
  border: 1px solid black;
  width: 128px;
  height: 128px;
}
#inner1
{
  width: 128px;
  height: 128px;
  background-position: left bottom 50%;
  background-image: url(aqua-32x32.png);
  background-repeat: no-repeat;
}
  </style>
</head>
<body>
<div id="outer"><div id="inner1"></div></div>
</body>
</html>