<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/css/bootstrap.min.css" integrity="sha384-rwoIResjU2yc3z8GV/NPeZWAv56rSmLldC3R/AZzGRnGxQQKnKkoFVhFQhNUwEyJ" crossorigin="anonymous">
</head>
<body>
<h1 class="text-center">Hello, world!</h1>
<div class="container">
<div class="row">
<div class="col-6 text-center">
<h2>example of col-6</h2>
</div>
<div class="col-6 text-center">
<h2>example of col-6</h2>
</div>
</div>
</div>
</body>
</html>