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What You Should Already Know
Before you continue you should have some basic understanding of
the following:
· WWW, HTML and the basics of building Web pages
If you want to study these subjects first, before you start
reading about CSS.
What is 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
CSS Demo
With CSS, your HTML documents can be displayed using different
output styles:
Styles Solve a Common Problem
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.
Both Netscape 4.0 and Internet Explorer 4.0 support Cascading
Style Sheets.
S tyle Sheets Can Save a Lot of Work
Styles in HTML 4.0 defines how HTML elements are displayed, just
like the font tag and the color attribute in HTML 3.2. Styles
are normally saved in files external to your HTML documents.
External style sheets enable you to change the appearance and
layout of all the pages in your Web, just by editing a single
CSS document. If you have ever tried to change the font or color
of all the headings in all your Web pages, you will understand
how CSS can save you a lot of work.
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.
Multiple Styles Will Cascade Into One
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.
Cascading Order
What style will be used when there is more than one style
specified for an HTML element?
Generally speaking we can say that all the styles will "cascade"
into a new "virtual" Style Sheet by the following rules, where
the highest number has the highest priority:
Browser default
External Style Sheet
Internal Style Sheet (inside the <head> tag)
Inline Style (inside HTML element)
So, an inline style (inside an HTML element) has the highest
priority, which means that it will override every style declared
inside the <head> tag, in an external style sheet, and in a
browser (a default value).
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