I have only the base KDE installed (sudo apt-get install plasma-desktop), not the entire kubuntu-desktop. Unfortunately GTK apps have the fugly Raleigh theme. I've installed QtCurve with sudo apt-get install qtcurve, but the GTK apps still have Raleigh theme. I assume I have to select the QtCurve theme somehow.
@13east has posted a picture of the settings dialog in his answer below. Unfortunately the GTK+ appearance is the only tab that is missing from my Settings Dialog. I assume this is because I've installed only plasma-desktop instead of the entire kubuntu-desktop. Is there a way to manually set the theme, perhaps by editing some configuration files?
Best Answer
If you open the "System Settings" app, there's an icon in the top row for something like "application settings" (I think it's second or third from the left in the top row--I don't have KDE available at the moment). If you click on that icon you'll see a dialogue with a few options in the left-hand panel. One of them is to set the theme for GTK applications. You should just be able to select qtcurve from the drop-down menu in the right-hand pane under that tab.