证明内容MD中心不起作用?

Question

我正在学习一个教程，我想在达到中等屏幕尺寸时使用justify-content-md-center。但它似乎不起作用。

<div class="container">
<div class="row" style="background:lightblue">
<div class="col-md-2">col-sm-6</div>
<div class="col-md-8">col-sm-6</div>
<div class="col-md-2">col-sm-6</div>
</div>
<div class="row justify-content-md-center">
<div class="col-md-2">col-sm-2</div>
<div class="col-md-2">col-sm-2</div>
<div class="col-md-2">col-sm-2</div>
</div>
</div>

感谢您的帮助

Answer 1

希望这有效

<link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/css/bootstrap.min.css" rel="stylesheet" />

<div class="row justify-content-center" style="background: darkgray;">
<div class="col-xs-2">
<img src="https://placehold.it/150x150" alt="sample image">
</div>

<div class="col-xs-2">
<img src="https://placehold.it/150x150" alt="sample image">
</div>
</div>