bootstrap 清除浮动

<div class="container">
<div class="row">

        <header id="main_header" class="col-md-12">

            <nav class="navbar navbar-default" role="navigation">

            </nav>

            <div class="contact pull-left">

            </div>        

        </header>
</div>
</div>

Bootstrap has pull-left and pull-right already to float content. clearfix shouldn't be needed if you are utilizing a container/row.

Realistically you could also (or instead) use the grid utilities on the nav/contact.

来自 http://stackoverflow.com/questions/24805039/how-to-clear-floats-properly-in-twitter-bootstrap