Hello Arvind,
Use following code to get complete (full height and width) background color of your page
<!DOCTYPE html>
<html lang="en" xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta charset="utf-8" />
<title></title>
<style type="text/css">
html {
margin: 2px;
padding: 0;
}
body {
font-size: .85em;
font-family: "Segoe UI", Verdana, Helvetica, Sans-Serif;
margin: 0;
padding: 0;
background-color:gray;
width:100%;
height:100%;
}
</style>
</head>
<body>
</body>
</html>