CSS was invented by Håkon Wium Lie on October 10, 1994, and maintained
through a group of people within the W3C called the CSS Working Group.
 The CSS Working Group creates documents called specifications.
When a specification has been discussed and officially ratified by
 W3C members, it becomes a recommendation.

These ratified specifications are called recommendations because
the W3C has no control over the actual implementation of the language.
 Independent companies and organizations create that software.

NOTE - The World Wide Web Consortium or W3C is a group that makes
recommendations about how the Internet works and how it should evolve.

CSS Versions
CSS Versions
Cascading Style Sheets, level 1 (CSS1) was came out of W3C as a
 a recommendation in December 1996. This version describes the CSS
language as well as a simple visual formatting model for all the HTML tags.

CSS2 became a W3C recommendation in May 1998 and builds on CSS1.
 This version adds support for media-specific style sheets e.g.
printers and aural devices, downloadable fonts, element positioning
and tables.

CSS3 became a W3C recommendation in June 1999 and builds on older versionsCSS. it has divided into documentation is called as modules andhere each module having new extension features defined in CSS2.

CSS3 Module
What is CSS?
CSS stands for Cascading Style Sheets
CSS describes how HTML elements are to be displayed on the screen, paper, or in other media
CSS saves a lot of work. It can control the layout of multiple web pages all at once
External stylesheets are stored in CSS files
advantages of CSS
CSS saves time - You can write CSS once and then reuse the same sheet in
multiple HTML pages. You can define a style for each HTML element and
 apply it to as many Web pages as you want.

Pages load faster - If you are using CSS, you do not need to write
HTML tag attributes every time. Just write one CSS rule of a tag and applyit to all the occurrences of that tag. So less code means ffaster downloadtimes.

Easy maintenance - To make a global change, simply change the style,
 and all elements in all the web pages will be updated automatically.

Superior styles to HTML - CSS has a much wider array of attributes
 than HTML, so you can give a far better look to your HTML page in
comparison to HTML attributes.

Multiple Device Compatibility - Style sheets allow content to be optimizedfor more than one type of device. By using the same HTML
document, different versions of a website can be presented for handhelddevices such as PDAs and cell phones or for printing.

Global web standards - Now HTML attributes are being deprecated and it is being recommended to use CSS. So it's a good idea to start using CSS in all the HTML pages to make them compatible withfuture browsers.
 Syntax
A CSS comprises of style rules that are interpreted by the browser and then applied to the corresponding elements in your document. A style rule is made of three parts -

Selector - A selector is an HTML tag at which a style will be applied.
This could be any tag like <h1> or <table> etc.

Property - A property is a type of attribute of HTML tag.
Put simply, all the HTML attributes are converted into CSS
properties. They could be color, border etc.

Value - Values are assigned to properties. For example,
color property can have value either red or #F1F1F1 etc.
Inline CSS