The Free On-line Dictionary of Computing (30 December 2018):

Cascading Style Sheets
CSS

    (CSS) An extension to HTML to allow styles,
   e.g. colour, font, size to be specified for certain elements
   of a hypertext document.  Style information can be included
   in-line in the HTML file or in a separate CSS file (which can
   then be easily shared by multiple HTML files).  Multiple
   levels of CSS can be used to allow selective overriding of
   styles.

   (http://w3.org/Style/CSS/).

   (2000-07-26)