<!DOCTYPE html>
<html>
<head>
<style>
#center {
margin: 0 auto;
border: 1px solid black;
width: 100px;
}
</style>
</head>
<body>
<div id="center"><h1>Center</h1></div>
</body>
</html>
<!DOCTYPE html>
<html>
<head>
<style>
#center {
margin: 0 auto;
border: 1px solid black;
width: 100px;
}
</style>
</head>
<body>
<div id="center"><h1>Center</h1></div>
</body>
</html>