[html] Apply style to cells of first row

It should be very simple but I can't figure it out.

I have a table like this :

<table class="category_table">
 <tr><td> blabla 1</td><td> blabla 2 </td></tr>
 <tr><td> blabla 3 </td><td> blabla 4 </td></tr>
</table>

I want to make td tags of first tr row have vertical-align. But not the second row.

.category_table td{
    vertical-align:top;
}

This should do the work:

.category_table tr:first-child td {
    vertical-align: top;
}

Below works for first tr of the table under thead

table thead tr:first-child {
   background: #f2f2f2;
}

And this works for the first tr of thead and tbody both:

table thead tbody tr:first-child {
   background: #f2f2f2;
}