<!DOCTYPE html>
<html>
    <head>
        <title>Bootstrap .clearfix 实例</title>
        <meta charset="utf-8">
        <meta name="viewport" content="width=device-width, initial-scale=1">
        <link rel="stylesheet" href="https://cdn.staticfile.org/twitter-bootstrap/3.3.7/css/bootstrap.min.css">  
        <script src="https://cdn.staticfile.org/jquery/2.1.1/jquery.min.js"></script>
        <script src="https://cdn.staticfile.org/twitter-bootstrap/3.3.7/js/bootstrap.min.js"></script>
    </head>
    <body>

        <div class="container-fluid">
            <h1>Hello World!</h1>
            <div class="row">
                <div class="col-xs-6 col-sm-3" style="background-color:lavender;">
                    列 1<br>
                    重置窗口大小,查看效果。也尝试删除有 clearfix  的 div 查看效果。
                </div>
                <div class="col-xs-6 col-sm-3" style="background-color:lavenderblush;">列 2</div>
                <!-- Add clearfix for only the required viewport -->
                <div class="clearfix visible-xs"></div>
                <div class="col-xs-6 col-sm-3" style="background-color:lightcyan;">列 3</div>
                <div class="col-xs-6 col-sm-3" style="background-color:lightgray;">列 4</div>
            </div>
        </div>

    </body>
</html>