You can get GTK themes from, for example, xfce-look.org gnome-look.org [http://browse.deviantart.com/?qh=§ion=&q=GTK+theme deviantart.com]
You only need to untar those themes under ~/.themes, so first:
$ mkdir ~/.themes
$ cd ~/.themes
$ tar -zxvf theme-name-here.tar.gz or
$ tar -jxvf theme-name-here.tar.bz2
Make sure you check the what engines the theme needs, usually with somethin like
$ grep engine ~/.themes/
You can most likely install them through your package manager, like:
# apt-get install gtk2-engines-pixbuf or
# apt-get install gtk2-engines-* or
# emerge gtk2-engines-pixbuf
You should get the idea.
Get gtk-theme-switch (note that there is also a version for GTK2) or gtk-chtheme. Then just fire 'em up and you should see a nice list of all styles. Just select the one you want to use and click Apply. You can also use LXAppearance to change the gtk-themes.
This shows you how to edit GTK settings without any extra application installed.
Install the GTK theme as shown above (extract theme to ~/.themes and icon set to ~/.icons).
Create or edit the ~/.gtkrc-2.0 file. In that file input parameters such as the following:
#sets the font
gtk-font-name = "sans 8"
#sets the theme
gtk-theme-name = "Clearlooks Crystal 1.1"
#sets the icon theme
gtk-icon-theme-name = "CrystalClear-GNOME-1.0.0"
#shows only icons in the toolbar
gtk-toolbar-style = GTK_TOOLBAR_ICONS
#shows small icons in the toolbar
gtk-toolbar-icon-size = GTK_ICON_SIZE_SMALL_TOOLBAR
#sets the background color in Rox back to white because some GTK themes set it to light gray
style "rox" = "default"
bg[NORMAL] = "#ffffff"
bg[ACTIVE] = "#ffffff"
widget_class "*Collection*" style "rox"
You can also use a different GTK theme, icon theme and fonts for specific GTK applications. If you just want to change the GTK theme, run your application with the following command:
$ GTK2_RC_FILES=/path/to/your/theme/gtkrc your_application
If you like to set a custom icon theme and font, create an empty file wherever you find convenient and call it whatever you want (for example, ~/.themes/custom.gtkrc). Then fill it with your different settings:
gtk-font-name = "sans 7"
gtk-theme-name = "niroki"
gtk-icon-theme-name = "SimplyGrey"
Now run the application with the following command:
$ GTK2_RC_FILES=/path/to/your/custom.gtkrc your_application
Add the command in your menu or launcher and enjoy.
To use GTK3 themes, edit (or create) the ~/.config/gtk-3.0/settings.ini file. Specify the theme you want with the gtk-theme-name parameter. For example, if you want to use the Adwaita theme, your settings.ini file should look like:
gtk-theme-name = Adwaita
gtk-icon-theme-name = SimplyGrey
gtk-fallback-icon-theme = gnome
gtk-font-name = Sans 10
# next option is applicable only if selected theme supports it
gtk-application-prefer-dark-theme = true
How to install fonts