Table 单双行交叉样式的显示

<style type="text/css">
.trSty{
    background-color: expression((this.sectionRowIndex%2==0) ? "#419C33" : "#CCEBC7")
}
</style>
<table id="main_table">
<tr class="trSty">
<td width="100">a</td>
<td width="100">b</td>
</tr>
<tr class="trSty">
<td width="100">a</td>
<td width="100">b</td>
</tr>
<tr class="trSty"> 
<td width="100">a</td>
<td width="100">b</td>
</tr>
<tr class="trSty"> 
<td width="100">a</td>
<td width="100">b</td>
</tr>
</table>