For more information about CSS, proceed to the next section. To start 

creating CSS right away, proceed to 

 Create a new style sheet  

on page 104

.

Learn about CSS

Cascading Style Sheets (CSS) are a collection of formatting rules that 

control the appearance of content on a web page. When you use CSS to 

format a page, you separate content from presentation. The content of 

your page the HTML code resides in the HTML file itself, while the 

CSS rules that define the presentation of the code reside in another file (an 

external style sheet) or in another part of the HTML document (usually 

the 

 section). With CSS you have flexibility and control over the 

exact appearance of your page, from precise positioning of layout to 

specific fonts and styles.

CSS lets you control many properties that cannot be controlled with 

HTML alone. For example, you can specify different font sizes and units 

(pixels, points, and so on) for selected text. By using CSS to set font sizes in 

pixels, you can also ensure a more consistent treatment of your page layout 

and appearance in multiple browsers.

A CSS formatting rule consists of two parts the selector and the 

declaration. The selector is a term (such as 

P

, 

H1

,

a class name, or an id) 

that identifies the formatted element, and the declaration defines what the 

style elements are. In the following example, 

H1

 is the selector, and 

everything that falls between the braces (

{}

) is the declaration:

H1 {

font size: 16 pixels;

font family: Helvetica;

font weight: bold;

}

The declaration consists of two parts, the property (such as 

font family

), 

and the value (such as 

Helvetica

). The preceding example creates a style 

for 

H1

 tags: The text for all 

H1

 tags linked to this style is 16 pixels in size, 

and uses Helvetica font and bold.

102 Tutorial: Formatting Your Page with CSS