The solution to this problem is simple. Thanks to the package qtcurve if you are using Kubuntu.
Step 1: Start konsole
sudo apt-get install qtcurve
Step 3: Go to System Settings -> Appearance -> GTK styles and fonts
Step4: In the GTK styles sub-menu select QtCurve
Step 5: Restart your GTK Apps. Enjoy the new sleek look 🙂