Wikipedia:TemplateStyles

TemplateStyles allow custom CSS pages to be used to style content without an interface administrator having to edit sitewide CSS. TemplateStyles make it more convenient for editors to style templates; for example, those templates for which the sitewide CSS for the mobile skin or another skin (e.g. Timeless) currently negatively affects the display of the template.

TemplateStyles work on all types of pages, not just templates, despite the name.