<html>
<head>
<link rel="stylesheet" type="text/css" href="style.css" media="all">
</head>
<body>
<div class="Center-Container">
<div class="Absolute-Center">
Выравние по центру
</div>
</div>
</body>
</html>.Center-Container {
position: relative;
}
.Absolute-Center {
width: 50%;
height: 50%;
overflow: auto;
margin: auto;
position: absolute;
top: 0; left: 0; bottom: 0; right: 0;
}