Bootstrap behavior

Can somebody explain what is going on here? I'm using bootstrap 3.3.7 This is body content Why .container elements are invisible?

    <!-- Navbar -->
    <div class="navbar navbar-inverse navbar-fixed-top">
        <div class="navbar-header">
            <a class="navbar-brand" href="#">Big Brother</a>
        </div>
        <div class="navbar-collapse">
            <ul class="nav navbar-nav">
                <li><a href="#" href="/">Home</a></li>
                <li><a href="#" href="/message">Messages</a></li>
            </ul>
            <ul class="nav navbar-nav navbar-right">
                <li>something</li>
            </ul>
        </div>
    </div>
    <div class="container">
        <h2>Invisible</h2>
    </div>