CSS3 :nth-child(odd) Selector not selecting columns not rows : I have a simple table using tr:nth-child(odd) to alternate background for rows in a table. 

HTML

    <tr class="sao-zebra">
    	<th class="sao-feature">Some Text</th>
    	<td class="sao-even-basic">Copy</td>
    	<td class="sao-even-gold">Copy</td>
    </tr>
    <tr class="sao-zebra">
    	<th class="sao-feature">More Text</th>
    	<td class="sao-odd-basic"><span class="sao-checkmark">&check;</span></td>
    	<td class="sao-odd-gold"><span class="sao-checkmark">&check;</span></td>
    </tr>

CSS

    tr.sao-zebra :nth-child(odd) {
      background: #23282D;
    }

as is stands, the table has 3 columns. The nth-child pseudo selector is causing every other column to be black, not every other row. What have I done wrong?