CSS provides the tool to design and create a great looking web or Windows 8 applications with reusability across all pages.
The principal of Css has root in Standardized Generalized Markup Language (SGML) . Its goal is to create a consistent look across the web-pages and to separate structure from presentation so you can provide different style sheets for printing, browsing, and other sections. The World Wide Web Consortium (W3C) published different level of CSS like CSS Level 1, 2, 3 etc.
Cascading style sheets provides a means to apply presentation to as HTML structure by defining how HTML elements are displayed . By Using CSS you can set background and fore-ground colors, margins, border, padding, fonts, positions and much more . You have creative control of HTML elements, so you can decide what the elements can look like and where the display on the screen.
A style is a rule that describe how to format a specific part of an HTML document.
Style can be made to apply specific HTML elements based on selector .You can use selector to locate and select elements by name, class, ID etc. You can also create style that work only with Image , and you can create style that work only with hyperlinks . You an also create named style sheet that apply to any element. The re usability is powerful.