如何将html表格分成两部分？

<table>
  <tr>
    <td>单元格1</td>
    <td>单元格2</td>
  </tr>
  <tr>
    <td>单元格3</td>
    <td>单元格4</td>
  </tr>
</table>

table {
  border-collapse: collapse;
}

td {
  border: 1px solid black;
  padding: 10px;
}

td:nth-child(1) {
  background-color: #f0f0f0;
}

<style>
  table {
    border-collapse: collapse;
  }

  td {
    border: 1px solid black;
    padding: 10px;
  }

  td:nth-child(1) {
    background-color: #f0f0f0;
  }
</style>

<table>
  <tr>
    <td>单元格1</td>
    <td>单元格2</td>
  </tr>
  <tr>
    <td>单元格3</td>
    <td>单元格4</td>
  </tr>
</table>