CSS Introduction

What You Should Already Know

Before you continue you should have a basic understanding of the following:

• HTML

If you want to study this subject first, find the tutorial on our Home page.

CSS Demo - One Page - Multiple Styles!

One HTML page displayed with different style sheets: See how it works!

What is CSS?

• CSS stands for Cascading Style Sheets
• CSS defines how HTML elements are to be displayed
• Styles were added to HTML 4.0 to solve a problem
• CSS saves a lot of work
• External Style Sheets are stored in CSS files

CSS Solved a Big Problem

HTML was NEVER intended to contain tags for formatting a document.

HTML was intended to define the content of a document, like:

<h1>This is a heading</h1>

<p>This is a paragraph.</p>

When tags like <font>, and color attributes were added to the HTML 3.2 specification, it started a nightmare for web developers. Development of large web sites, where fonts and color information were added to every single page, became a long and expensive process.

To solve this problem, the World Wide Web Consortium (W3C) created CSS.

In HTML 4.0, all formatting could (and should!) be removed from the HTML document, and stored in a separate CSS file.

CSS Saves a Lot of Work!

The style definitions are normally saved in external .css files.

With an external style sheet file, you can change the look of an entire Web site by changing just one file!

CSS Introduction

原文：http://www.cnblogs.com/eobd2/p/4251901.html