CSS ::Before on Table Cell

I want to add a ::before selector on some table cells what has a position:absolute , but it fails:

table{ border:1px solid #ccc; padding:10px; }
table td{ border:1px solid #ccc; padding:5px; }

.useBefore::before{
  content:'before';
  position:absolute;
}

<table>
       <tbody>
         <tr>
           <td>bird</td>
           <td>animal</td>
           <td>nature</td>
        </tr>
        <tr class='useBefore'>
           <td>building</td>
           <td>robot</td>
           <td>city</td>
        </tr>
      </tbody>
  </table>

I noticed that if I add the ::before to all of the tr's then it works:

table开发者_如何转开发{ 
    border:1px solid #ccc; 
    padding:10px;
  }
  table td{
    border:1px solid #ccc;
    padding:5px;
  }
  
  tr::before{
    content:'before';
    position:absolute;
  }

<table>
    <tbody>
      <tr>
        <td>bird</td>
        <td>animal</td>
        <td>nature</td>
      </tr>
      <tr class='useBefore'>
        <td>building</td>
        <td>robot</td>
        <td>city</td>
      </tr>
    </tbody>
  </table>

But this is not what I want, because I want to add it only on some of them.

---

I'm not sure why it fails exactly, but you could add it on the first table cell instead.

  .useBefore td:first-child:before{
    content:'before';
    position:absolute;
  }