A style sheet dictates the layout of pages and the content elements to be inserted into such layout, and is independent of the actual language used for page rendition.
This accommodates the use of proprietary elements so long as those elements can be presented to the intended audience through complete style sheet definitions (including aural/speech and tactile styles).
Templates are processed by a template processor, a template engine which produces a web document and a style sheet used for page layout of the document.