You use the Themes tab on the Appearance Preferences tool to select or customize a theme (System | Preferences | Appearance). Themes control your desktop appearance. The Themes tab will list icons for currently installed themes The icons show key aspects or each theme such as window, folder, and button images, in effect previewing the theme for you.
The Ubuntu theme is initially selected. You can move through the icons to select a different theme if you wish. If you have downloaded additional themes from http://art.gnome.org, you can click the install button to locate and install them. Once installed, the additional themes will also be displayed in the Theme tab. If you download and install a theme or icon set from the Ubuntu repository, it will be automatically installed for you. Three new themes have been added: Dust, Dust Sand, and New Wave. If you installed the Ubuntu Studio desktop, there also will be an UbuntuStudio theme.
The true power of Themes is shown its ability to let users customize any given theme. Themes are organized into four components: controls, colors, window border, icons, and pointer. Controls covers the appearance of window and dialog controls like buttons and slider bars. Window border lets you choose title bars, borders, window buttons sets. Icons lets you choose different icon sets. Pointers provides different pointer sets to use. Colors lets you choose the background and text color for windows, input boxes, selections, and tool tips. You can even download and install separate components like specific icon sets, which you can then use in a customized theme.
Clicking the Customize button opens a Themes Details window with tabs for different theme components. The components used for the current theme are selected by default. A color tab lets you set the background and text colors for windows, input boxes, and selected items. In the control, window border, and icon tabs you will see listings of the different themes. You can then mix and match different components from those themes, creating your own customized theme, using window borders from one theme and icons from another. Upon selecting a component, your desktop changes automatically showing you how it looks. If you have added a component, like a new icon set, it also is shown.
Once you have created a new customized theme, a Custom Theme icon appears in the list on the Theme tab. To save the customized theme, click the Save As button. This opens a dialog where you can enter the theme name, any notes, and specify whether you also want to keep the theme background.
Customized themes and themes installed directly by a user are placed in the .themes directory in the user’s home directory. Should you want these themes made available for all users, you can move them from the .themes directory to the /usr/share/themes directory. In a terminal window run a cp command as shown here for the mytheme theme. The operation requires administrative access (sudo).
sudo cp -r .themes/mytheme /usr/share/themes
You can do the same for icon sets you have downloaded. Such sets will be installed in the user’s .icons directory. You can then copy them to the /usr/share/icons directory to make them available to all users.
TIP: You can set your screen resolution as well as screen orientation using the Monitors Preferences utility accessible from System | Preferences | Monitors. The utility supports RandR screen management features like screen rotation, resolution, and refresh rate.