bootstrap: 移动模式下行与行之间的空格

bootstrap: spaces between rows in mobile mode

我有一个page

我只想在移动模式下也保留行与行之间的空格。我尝试使用 visible-sm class

添加分隔符
<div class="row">
    <div class="col-xs-6 col-sm-6  col-md-3">
        Block #11
    </div>

    <div class="col-xs-6 col-sm-6  col-md-3">
        Block #12
    </div>

    <div class="w-100 visible-sm row-divider"></div>

    <div class="col-xs-6 col-sm-6  col-md-3">
        Block #13
    </div>

    <div class="col-xs-6 col-sm-6  col-md-3">
        Block #14
    </div>
</div>

但这并没有帮助。我应该如何处理在移动和桌面模式下看起来相似的行?

我将边距从行移到了列。

http://jsfiddle.net/aq9Laaew/147947/

h3{
  margin-bottom:-20px;
}

div[class^='col'] {
  background: #f8f9fa;
  margin-top: 40px;
}

.col {
  border: solid 1px #6c757d;
  padding: 10px;
}
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css" integrity="sha384-MCw98/SFnGE8fJT3GXwEOngsV7Zt27NXFoaoApmYm81iuXoPkFOJwJ8ERdknLPMO" crossorigin="anonymous">
<script src="https://code.jquery.com/jquery-3.3.1.slim.min.js" integrity="sha384-q8i/X+965DzO0rT7abK41JStQIAqVgRVzpbzo5smXKp4YfRvH+8abtTE1Pi6jizo" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.3/umd/popper.min.js" integrity="sha384-ZMP7rVo3mIykV+2+9J3UJ46jBk0WLaUAdn689aCwoqbBJiSnjAK/l8WvCWPIPm49" crossorigin="anonymous"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/js/bootstrap.min.js" integrity="sha384-ChfqqxuZUCnJSK3+MXmPNIyE6ZbWh2IMqE241rYiqJxyMiZ6OW/JmZQ5stwEULTy" crossorigin="anonymous"></script>
<div class="container">
    <h3>Block #1</h3>
    <div class="row">
        <div class="col-xs-6 col-sm-6  col-md-3">
            Block #11
        </div>

        <div class="col-xs-6 col-sm-6  col-md-3">
            Block #12
        </div>
       

        <div class="col-xs-6 col-sm-6  col-md-3">
            Block #13
        </div>

        <div class="col-xs-6 col-sm-6  col-md-3">
            Block #14
        </div>
    </div>
    <div class="row row-divider">
        <div class="col-xs-6 col-sm-6  col-md-3">
            Block #21
        </div>

        <div class="col-xs-6 col-sm-6  col-md-3">
            Block #22
        </div>

        <div class="col-xs-6 col-sm-6  col-md-3">
            Block #23
        </div>

        <div class="col-xs-6 col-sm-6  col-md-3">
            Block #24
        </div>
    </div>
    <div class="row row-divider">
        <div class="col-xs-6 col-sm-6  col-md-3">
            Block #31
        </div>

        <div class="col-xs-6 col-sm-6  col-md-3">
            Block #32
        </div>

        <div class="col-xs-6 col-sm-6  col-md-3">
            Block #33
        </div>
    </div>
</div>