ИСХОДНЫЙ КОД<!DOCTYPE html>
<html lang="en">
<head>
<!-- Required meta tags -->
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<!-- Bootstrap CSS -->
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/css/bootstrap.min.css">
<link href="css/style.css" rel="stylesheet">
</head>
<body>
<div calss="container-fluid">
<div class="row">
<div class="col-md-4"></div>
<div class="col-md-4"></div>
<div class="col-md-4"></div>
</div>
</div>
<!-- jQuery first, then Tether, then Bootstrap JS. -->
<script src="https://code.jquery.com/jquery-3.2.1.slim.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/tether/1.4.0/js/tether.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/js/bootstrap.min.js"></script>
</body>
</html>
ФАЙЛ style.css. row div {
padding: 300px;
background-color: lighten(#000, 20%);
}
Средний
Средний
