Introduction to CSS
What You Should Already Know
Before you continue you should have some basic understanding of the
following:
If you want to study this subject first, find the tutorials on our
Home page.
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:
See how it works
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.
All major browsers support Cascading Style Sheets.
Style Sheets Can Save a Lot of Work
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.
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 number four
has the highest priority:
- Browser default
- External style sheet
- Internal style sheet (inside the <head> tag)
- Inline style (inside an HTML element)
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).
Note: If the external style sheet link is placed below the internal
style sheet in HTML <head>, the external style sheet will override the internal
style sheet.
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