The concept of style sheets didn't originate with graphical user interfaces, it was a concept that originated in the publishing industry around half a century ago. The concept wasn't seen to be restricted to text, either. Here is a paper from 1983 that discusses the concept of graphical style sheets:
https://research.tableau.com/sites/default/files/Graphical%20Style.pdfThe application of style sheets passed from the publishing industry into word processing. Style sheets were quickly incorporated into many word processing products. Microsoft Word has used style sheets since the early days of Windows.
The concept of cascading style sheets was taken up as a matter of course by WWW developers who were very familiar with the concept of style sheets from their use in word processing.
However, more important in the context of this discussion is the application of style sheets for the production of graphics in the graphics industry. A number of companies developing software in the graphics industry are starting to integrate style sheets into their products, including Adobe:
https://helpx.adobe.com/in/illustrator/using/graphic-styles.htmlAn interesting application is the integration of style sheets in mapping software by Cartotype. Initial steps have also been taken towards incorporating style sheets into Inkscape.