<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<style type="text/css">
.header,.main,.footer{
500px;
}
.header,.footer{
height: 100px;
background: #000;
}
</style>
</head>
<body>
<div class="header"></div>
<div class="main></div>
<div class="footer"></div>
</body>
</html>