1. Open a terminal window
2. Type this command to open the GTK preferences file and create one if you don't already have one:
3. Paste these lines in the kwrite window:
gtk-icon-sizes = "gtk-menu=8,8:
gtk-toolbar-style = GTK_TOOLBAR_ICONS
gtk-font-name = "DejaVu Sans 8"
4. Save and close. Start an application like Skype, and voila !