Bootstrap 4

HTML

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.2/css/bootstrap.min.css">
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.2/js/bootstrap.min.js"></script>
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootswatch/3.3.7/flatly/bootstrap.min.css">
<div class="container">
    <div class="navbar navbar-default">
        <div class="navbar-header">
            <a class="navbar-brand" href="#">Bootstrap 4 plus Flatly theme</a>
        </div>        
    </div>
   
    <div class="jumbotron">
        <h1>Twitter Bootstrap 4.0 + Flatly</h1>
        <p class="lead">Starter template with CSS and JS included.</p>
        <p><a class="btn btn-lg btn-info" href="#fork">Fork this fiddle</a></p>
      </div>
</div>

CSS

body {
    margin: 0px;
}

div.container {
    background-color: lightgreen !important; 
}