A few things to try.
First you are using a DetailsView not a GridView, maybe it should be a GridView?
Set EnableTheming to false on the Details/GridView and see if that makes the css class show up.
If not you could just wrap a div around the Details view with class="ace_signup", then change your css selectors to
.ace_signup table {}
.ace_signup tr {}
In Xhtml, always use lower case element names never upper case, so things in your CSS like TABLE.ace_signup should be table.ace_signup
Hope it helps,
Joe