如何在flex-box表中添加行？

<div class="flex-container">
  <div class="header-container">
    <div class="header-cell">表头1</div>
    <div class="header-cell">表头2</div>
    <div class="header-cell">表头3</div>
  </div>
  <div class="content-container">
    <div class="row">
      <div class="cell">内容1</div>
      <div class="cell">内容2</div>
      <div class="cell">内容3</div>
    </div>
    <div class="row">
      <div class="cell">内容4</div>
      <div class="cell">内容5</div>
      <div class="cell">内容6</div>
    </div>
  </div>
</div>

.flex-container {
  display: flex;
  flex-direction: column;
}

.header-container {
  display: flex;
  flex-direction: row;
}

.header-cell {
  flex-grow: 1;
  border: 1px solid black;
}

.content-container {
  display: flex;
  flex-direction: column;
}

.row {
  display: flex;
  flex-direction: row;
}

.cell {
  flex-grow: 1;
  border: 1px solid black;
}