@edspencer Thank you for clarifying this. I've read that theming guide a number of times, but it doesn't go into much depth.
I'm working on a custom theme that uses a special background image for active tabs. I sliced the background image myself, then to override the default CSS for tabs I added my own CSS for modern browsers, and then overrode that CSS with IE-specific CSS activated by conditional comments. This is pretty much how I've always done theming in Ext JS.
Am I doing it the hard way? Would the slicer tool save me a lot of this effort?