Unable to set table th and td width

I have a table that is 2 rows and 12 columns. The first row is th columns and the second is just td columns. I have the table set to 100% width, but it’s nested inside of a div that is set to 935px wide and with an overflow value of hidden. I’m trying to set the td and th width using css, but they’re not adjusting.

I’m giving the table itself a class of “historytable” and then in my css file I’m setting .historytable th {width:300px;} and .historytable td {width:300px;} , but it’s not working. Any idea why? The page can be viewed at www.ts24.com/dev/2009/history.cfm. Thanks!

Jesse