You can use themes to modify and control the appearance of the desktop in a consistent manner. A theme is a group of coordinated settings that specifies how a desktop component or a group of desktop components appears. When you apply a theme, the system modifies many desktop components simultaneously to achieve the desired effect. For example, if you apply a theme that increases the font size across the desktop, the theme also modifies the size of panels and icons on the desktop for optimum compatibility with the font size.
The following types of themes affect different parts of the desktop:
Desktop themes determine the visual appearance of all windows, applications, dialogs, panels, and applets. Desktop themes also determine the visual appearance of the GNOME-compliant interface items that appear on windows, panels, and applets, such as menus, icons, and buttons. Some of the desktop themes that are available in the desktop are designed for special accessibility needs.
Window frame themes determine the appearance of the frames around windows only.
Nautilusfile manager themes
Nautilus file manager themes
determine the appearance of desktop background objects,
Nautilus icons, and the font used on tabs in the
Nautilus side pane.