A User interface stylesheet language is a

stylesheet language A style sheet language, or style language, is a computer language that expresses the presentation of structured documents. One attractive feature of structured documents is that the content can be reused in many contexts and presented in various w ...

which is meant to be applied to graphical computer user interfaces. They primarily act as subsidiary languages to style UI elements which are either programmed or marked-up (as in XML-based markup languages).

Examples

* Cascading Style Sheets as used in

Mozilla Mozilla is a free software community founded in 1998 by members of Netscape. The Mozilla community uses, develops, publishes and supports Mozilla products, thereby promoting free software and open standards. The community is supported institution ...

's XUL user interface * Qt Style Sheets as used in KDE4
Robert Staudinger's
CSS theming for

GTK+ GTK (formerly GIMP ToolKit and GTK+) is a free software cross-platform widget toolkit for creating graphical user interfaces (GUIs). It is licensed under the terms of the GNU Lesser General Public License, allowing both free and proprietary s ...

''Ars Technica article''
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References

Stylesheet languages {{Tech-stub