<!DOCTYPE html>
<html lang="en-US">
<head>
<style>
body{
height:100px;
border:1px solid green;
}
#point{
height:50%;
border:1px solid #000;
}
</style>
</head>
<body>
<div id="point">
Height of this container (div) is 50% of body.
</div> </body>
</html>