<!DOCTYPE>
<html>
<head>
<style>
#a {
border: 1px solid red;
height: 300px;
width: 300px;
margin: 0 auto;
}
</style>
</head>
<body>
<div id="a">
fafdafasfa dasfaf aadsfsas dasfas
</div>
</body>
</html>