scroll tbody

HTML

<div>
  <table>
    <thead>
      <tr>
        <th>head</th>
        <th>head</th>
        <th>head</th>
        <th>head</th>
        <th>head</th>
      </tr>
    </thead>
    <tbody>
      <tr>
        <td>body</td>
        <td>body</td>
        <td>body</td>
        <td>body</td>
        <td>body</td>
      </tr>
      <tr>
        <td>body</td>
        <td>body</td>
        <td>body</td>
        <td>body</td>
        <td>body</td>
      </tr>
      <tr>
        <td>body</td>
        <td>body</td>
        <td>body</td>
        <td>body</td>
        <td>body</td>
      </tr>
      <tr>
        <td>body</td>
        <td>body</td>
        <td>body</td>
        <td>body</td>
        <td>body</td>
      </tr>
      <tr>
        <td>body</td>
        <td>body</td>
        <td>body</td>
        <td>body</td>
        <td>body</td>
      </tr>
      <tr>
        <td>body</td>
        <td>body</td>
        <td>body</td>
        <td>body</td>
        <td>body</td>
      </tr>
    </tbody>
  </table>
</div>

CSS

thead,
tbody {
  display: block;
}

thead {
  text-align: left;
}

tbody {
  background: yellow;
  overflow-y: auto;
  height: 6em;
}

thead th,
tbody td {
  width: 4em;
  padding:2px;
}

thead tr th:first-child,
tbody tr td:first-child {
 
  width: 18em;
  background: salmon;
  font-weight: normal;
}