What You Should Already Know Before you continue you should have some basic understanding of the following: 在继续前你应该具备相关的基础知识：HTML / XHTML
What is CSS? 什么是CSS？ CSS stands for Cascading Style Sheets Styles define how to display HTML elements Styles are normally stored in Style Sheets Styles were added to HTML 4.0 to solve a problem External Style Sheets can save you a lot of work External Style Sheets are stored in CSS files Multiple style definitions will cascade into one
HTML tags were originally designed to define the content of a document. They were supposed to say "This is a header", "This is a paragraph", "This is a table", by using tags like <h1>, <p>, <table>, and so on. The layout of the document was supposed to be taken care of by the browser, without using any formatting tags. As the two major browsers - Netscape and Internet Explorer - continued to add new HTML tags and attributes (like the <font> tag and the color attribute) to the original HTML specification, it became more and more difficult to create Web sites where the content of HTML documents was clearly separated from the document's presentation layout. To solve this problem, the World Wide Web Consortium (W3C) - the non profit, standard setting consortium, responsible for standardizing HTML - created STYLES in addition to HTML 4.0. All major browsers support Cascading Style Sheets.
Styles sheets define HOW HTML elements are to be displayed, just like the font tag and the color attribute in HTML 3.2. Styles are normally saved in external .css files. External style sheets enable you to change the appearance and layout of all the pages in your Web, just by editing one single CSS document! CSS is a breakthrough in Web design because it allows developers to control the style and layout of multiple Web pages all at once. As a Web developer you can define a style for each HTML element and apply it to as many Web pages as you want. To make a global change, simply change the style, and all elements in the Web are updated automatically.
Style sheets allow style information to be specified in many ways. Styles can be specified inside a single HTML element, inside the <head> element of an HTML page, or in an external CSS file. Even multiple external style sheets can be referenced inside a single HTML document. 样式表答应样式信息用多种方式来定义.样式可以在一单独的HTML元素中指定,在<head>元素中或在一外部CSS文件中.甚至多个外部样表能集中在一个单一的HTML文档中
Cascading order
What style will be used when there is more than one style specified for an HTML element? 当多于一种的样式指定一HTML元素时使用怎样的样式呢?
Generally speaking we can say that all the styles will "cascade" into a new "virtual" style sheet by the following rules, where number four has the highest priority: 一般说来所有样式有下面的规则(第四个最有优先性)
Browser default 浏览器默认 External style sheet 外部样式表 Internal style sheet (inside the <head> tag) 内嵌样式表(在<head>标签内) Inline style (inside an HTML element) 行内样式(在一HTML元素内) So, an inline style (inside an HTML element) has the highest priority, which means that it will override a style declared inside the <head> tag, in an external style sheet, or in a browser (a default value). 所以写在HTML元素中的样式有最高的优先权(写在HTML元素内的),它会替代其他形式的样式.
