弹性盒两列包装

Question

我正在尝试转换利用flexbox提供2列包装的卡。

示例：

[1] [2]
[3] [4]
[5] [6]

目前，我认为目前所有阅读的内容都无法实现：

[1] [4]
[2] [5]
[3] [6]

我尝试了以下操作，但不幸的是，我似乎无法使侧边选项自动运行。

.card-columns-extra {
    column-count: 2;
    column-gap: 1.25rem;
    orphans: 1;
    widows: 1;
    flex-direction: column;
    flex-wrap: wrap;
    justify-content: flex-start;
    align-content: space-between;
    align-items: flex-start;
}

.card {
    width: 100%;
    position: relative;
    display: flex;
    flex-direction: column;
    min-width: 0;
    word-wrap: break-word;
}

<link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" rel="stylesheet"/>
<div class="container">
  <div class="card-columns-extra">
    <div class="card">
      <img class="card-img-top" src="http://via.placeholder.com/1600x900/483D8B/ffffff?text=Card+1" alt="Card image cap">
      <div class="card-body">
        <h5 class="card-title">Card title that wraps to a new line</h5>
        <p class="card-text">This is a longer card with supporting text below as a natural lead-in to additional content. This content is a little bit longer.</p>
      </div>
    </div>
    <div class="card p-3">
      <blockquote class="blockquote mb-0 card-body">
        <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer posuere erat a ante.</p>
        <footer class="blockquote-footer">
          <small class="text-muted">
            Someone famous in <cite title="Source Title">Source Title</cite>
          </small>
        </footer>
      </blockquote>
    </div>
    <div class="card">
      <img class="card-img-top" src="http://via.placeholder.com/1600x450/9400D3/ffffff?text=Card+2" alt="Card image cap">
      <div class="card-body">
        <h5 class="card-title">Card title</h5>
        <p class="card-text">This card has supporting text below as a natural lead-in to additional content.</p>
        <p class="card-text"><small class="text-muted">Last updated 3 mins ago</small></p>
      </div>
    </div>
    <div class="card bg-primary text-white text-center p-3">
      <blockquote class="blockquote mb-0">
        <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer posuere erat.</p>
        <footer class="blockquote-footer">
          <small>
            Someone famous in <cite title="Source Title">Source Title</cite>
          </small>
        </footer>
      </blockquote>
    </div>
    <div class="card text-center">
      <div class="card-body">
        <h5 class="card-title">Card title</h5>
        <p class="card-text">This card has supporting text below as a natural lead-in to additional content.</p>
        <p class="card-text"><small class="text-muted">Last updated 3 mins ago</small></p>
      </div>
    </div>
    <div class="card">
      <img class="card-img" src="http://via.placeholder.com/1600x1600/FF1493/ffffff?text=Card+3" alt="Card image">
    </div>
    <div class="card p-3 text-right">
      <blockquote class="blockquote mb-0">
        <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer posuere erat a ante.</p>
        <footer class="blockquote-footer">
          <small class="text-muted">
            Someone famous in <cite title="Source Title">Source Title</cite>
          </small>
        </footer>
      </blockquote>
    </div>
    <div class="card">
      <div class="card-body">
        <h5 class="card-title">Card title</h5>
        <p class="card-text">This is a wider card with supporting text below as a natural lead-in to additional content. This card has even longer content than the first to show that equal height action.</p>
        <p class="card-text"><small class="text-muted">Last updated 3 mins ago</small></p>
      </div>
    </div>
  </div>
</div>