jQueryUI selectable: can't apply theme??

jQueryUI selectable: can't apply theme??

I am developing an application using jQueryUI. I am also using the Themeroller. I want to have as many of my styles as possible defined using the theme, so that if I need to change some styles, I simply have to create a new custom theme (or download an existing theme).

I am trying to use the "selectable" widget in jQueryUI. It is working as it should - in Firebug I can see the "ui-selected" class being applied to the element that I select. However, there is no visual cue that the item has been selected. I looked in the theme CSS file (jquery-ui-1.8rc3.custom.css, which I downloaded from the Themeroller page), and I see no declaration for the "ui-selected" class. When I downloaded jQueryUI and the theme, I checked every option, including the one for "selectable".

How can I make my theme define the "ui-selected" class? Obviously, I could just create my own style declaration, but that solution is not ideal if I ever want to change the theme.