A Cascading Style Sheet (or CSS for short) is a term used in web page design that refers to a file that controls the presentation (for example fonts, colors, and spacing) of a web site. This enables the web page designer to separate document content from document presentation. This separation will simplify updating content when it changes and provide more flexibility and control in how the page will appear to the customer.

Customers often use a local CSS file to define colors, fonts, layout, and other aspects of document presentation that enhance readability or usability when they need it. Using CSS allows a superior user experience that puts the visitor in control.

CSS can also allow the web page to be presented in different styles for different rendering methods, such as on-screen, in print (after printing a web page), by voice (when read out by a speech-based browser or screen reader) and on Braille-based, tactile devices.

Redline Web Designs recommends the use of CSS especially to provide a print optimized version of the site and to simplify site redesign in the future. The use of CSS is widely accepted and has greatly enhanced the readability of web page content.