Cascading Style Sheets is a style sheet language used to describe the presentation display of a document written in a markup language, like HTML. Its most common application is to style web pages written in HTML and XHTML, but CSS can also be applied to any kind of XML document.
The principle design of CSS is to enable the separation of document content from its presentation, including elements such as the layout, colors, and fonts, all in a different file separated from the main content file. This separation can improve content accessibility, provide more flexibility and control in the specification of presentation characteristics, enable multiple pages to share formatting, reduce complexity and repetition in the structural content, and make the overall presentation of the content look more professional. CSS can also allow the same markup page to be presented in different styles for different rendering methods. While the author of a document typically links that document to a CSS document, viewers can use a different style sheet, perhaps one on their own computer, to override the one the author has specified.
CSS specifies a priority scheme to determine which style rules apply if more than one rule matches against a particular element. In this so-called cascade, priorities or weights are calculated and assigned to rules, so that the results are predictable.
In order to create a CSS document, users will need to first figure out if they are using a PC or a Mac.
For PC users:
- Go to your Start Menu, into All Programs, then Accessories. Search for the application program called Notepad. Open the program.
For Mac users:
- Download the TextWrangler program. After installing it, open up Finder, go to Applications, and search program by name. Open the program.
After you have opened the correct text-editing program, save the file with a filename extension of
.css. That will make this document a CSS document which you can edit to design the particular layout for your webpage.
CSS has various levels and profiles. Each level of CSS builds upon the last, typically adding new features and typically denoted as CSS1, CSS2, and CSS3. Profiles are typically a subset of one or more levels of CSS built for a particular device or user interface. Currently there are profiles for mobile devices, printers, and television sets. Profiles should not be confused with media types, which were added in CSS2.
CSS 1 Edit
The first CSS specification to become an official W3C Recommendation is CSS level 1, published in December 1996. Among its capabilities are support for:
- Font properties such as typeface and emphasis
- Color of text, backgrounds, and other elements
- Text attributes such as spacing between words, letters, and lines of text
- Alignment of text, images, tables and other elements
- Margin, border, padding, and positioning for most elements
- Unique identification and generic classification of groups of attributes
The W3C no longer maintains the CSS1 Recommendation.
CSS 2 Edit
CSS level 2 was developed by the W3C and published as a Recommendation in May 1998. A superset of CSS1, CSS2 includes a number of new capabilities like absolute, relative, and fixed positioning of elements, the concept of media types, support for aural style sheets and bidirectional text, and new font properties such as shadows. The W3C maintains the CSS2 Recommendation.
CSS level 2 revision 1 or CSS 2.1 fixes errors in CSS2, removes poorly-supported features and adds already-implemented browser extensions to the specification. While it was a Candidate Recommendation for several months, on June 15, 2005 it was reverted to a working draft for further review. It was returned to Candidate Recommendation status on 19 July 2007.
CSS 3 Edit
CSS level 3 has been under development since December 15, 2005. The W3C maintains a CSS3 progress report. CSS3 is modularized and consists of several separate recommendations.
There is no single CSS4 specification and there is no standard which named as CSS4. But a few level 4 modules exist such as Image Values, Backgrounds & Borders, or Selectors etc., which build on the functionality of a preceding level 3 module.
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