Disable theme for jQuery UI?

Disable theme for jQuery UI?

I haven't used jQuery much lately but I've used the tabs on many active sites. When I built them I was using jQuery UI with no theme , but the sites are now loading a default theme that's completely disrupting my custom styles for the tabs. I've searched exhaustively and can't find any version of jquery-ui.js that doesn't load jquery-ui.css as well and can't find any way to get around the default styles.

How can I completely disable any external theming without manually overriding each style in my own css? Is this a bug? Even when I tried to customize my own download and selected "No theme" I still ended up with the default styles.