Using text-align center in colgroup

I have a table in my page. I use colgroups to format all cells in this column the same way. It works well for background color and all. but I cannot seem to figure out why text-align center does not work. It does not align the text centered.

Example:

<table id="myTable" cellspacing="5"><colgroup id="names"></colgroup><colgroup id="col20" class="datacol"></colgroup><colgroup id="col19" class="datacol"></colgroup><colgroup id="col18" class="datacol"></colgroup><thead><th>&nbsp;</th><th>20</th><th>19</th><th>18</th></thead><tbody><tr><td>&nbsp;</td><td>&nbsp;</td><td>&nbsp;</td><td>&nbsp;</td></tr></tbody></table>

CSS:

#names {    width: 200px;}#myTable .datacol {    text-align: center;    background-color: red;}