.CSS File

The css file extension is associated with Cascading Style Sheets (CSS). The css files are used to format the contents of web pages.

A css file contains customized, global properties and other information about how to display HTML elements. It can define the size, background, colors, fonts, line spacing, indentation, borders, formats and location of HTML elements.

Basically, the css files are used to create a similar look and feel across whole websites. The .css files are also used to reduce the amount of work and HTML code generated by consolidating display properties into one single file. The .css files are stored in a plain text format.

The style sheets have existed in one form or another since the beginnings of SGML in the 1970s. Cascading Style Sheets were developed as a means for creating a consistent approach to providing style information for web documents.

The Cascading Style Sheets (CSS) helps Web developers create a uniform look for several pages within a Web site. Instead of defining the style of each table and each block of text within a page's HTML, commonly used styles need to be defined only once in a CSS document.
Once the style is defined in cascading style sheet, it can be used by any page that references the .css file. What more, the CSS allows to easy change styles across several pages at once.
For example, a Web developer is able to change the default font size from 12pt to 14pt for ten pages of his Web site at once. If the pages all reference to the same style sheet, the text size only needs to be changed on the style sheet and all the pages will have their font changed.

While Cascading Style Sheets are great for creating text styles, they are really helpful for formatting other aspects of the Web page layout as well. For example, the .css file can be used to define the cell padding of table cells, the style, thickness, and color of a table's border, and the padding around images or other objects. CSS gives Web developers much more control over how their web pages will look compared what the HTML format offers. For this very reason, most internet pages today incorporate cascading style sheets.

The CSS specifications are maintained by the World Wide Web Consortium (W3C).

MIME types:
text/css is registered for use with CSS by RFC 2318.

A css file extension is commonly used for text files that contain Cascading Style Sheets data, which are used on websites and define graphic layout and look of webpages.

How to open:

Use any suitable text editor or development suite to open or edit the .css files. You can also view the .css files with any modern internet browser.

How to convert:

You can convert HTML files to CSS with the use of some SEO tools available on the internet, such as TABLE2CSS.