<!DOCTYPE html>
<html lang="en-US">
<head>
<style>
body{
margin:0px !important;
}
div{
width:200px;
height:100vh;
background-color:#cccccc;
}
</style>
</head>
<body>
<div>
<p>Height of this div is exact equal to the height of this frame.</p>
<p>Try to resize the height of this window. 'vh' will calculate the height automatically.</p>
</div> </body>
</html>