umn-rule-style: solid;
    column-rule-width: 10px;

    row-rule-color: green;
    row-rule-style: solid;
    row-rule-width: 10px;

    flex-wrap: wrap;
  }

  .flex-item {
    background: skyblue;
    width: 50px;
  }
</style>
<div class="flex-container">
    <div class="flex-item"></div>
    <div class="flex-item"></div>
    <div class="flex-item"></div>
    <div class="flex-item"></div>
</div>
