              .col-xs-6 .col-sm-3
                                <br>调整窗口大小或者在手机上查看本示例
                            </div>
                            <div class="col-xs-6 col-sm-3">.col-xs-6 .col-sm-3</div>

                            <!-- Add the extra clearfix for only the required viewport -->
                            <div class="clearfix visible-xs"></div>

                            <div class="col-xs-6 col-sm-3">.col-xs-6 .col-sm-3</div>
                        