A CSS file is a cascading style sheet (CSS) file used to format the contents of a webpage. It contains customized, global properties for how to display HTML elements. CSS files can define the size, color, font, line spacing, indentation, borders, and location of HTML elements.

CSS file open in Adobe Dreamweaver CC 2017 CSS files are used to create a similar look and feel across websites. They also are used to reduce the amount of work and HTML code generated by consolidating display properties into a single file. CSS files are stored in a plain text format, which means you can open and edit them with any text editor. However, you should use web development programs, such as Dreamweaver and ColdFusion Builder, which provide more advanced features for editing CSS files.