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Cascading
Style Sheets
click here for Examples of CSS
click here for SCCC Web Site CSS
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What Is CSS?
CSS (cascading stylesheets) is a simple mechanism for controlling the style of a Web document without compromising its structure. By separating visual design elements (fonts, colors, margins, and so on) from the structural logic of a Web page, CSS give Web designers the control they crave without sacrificing the integrity of the data - thus maintaining its usability in multiple environments. In addition, defining typographic design and page layout from within a single, distinct block of code - without having to resort to image maps, <font> tags, tables, and spacer GIFs - allows for faster downloads, streamlined site maintenance, and instantaneous global control of design attributes across multiple pages.
Client-side support for the various CSS properties is uneven, even among browsers that support stylesheets. The CSS properties and values presented here are those supported by both Microsoft Internet Explorer 4 and Netscape Navigator 4.
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How CSS Works
CSS overrides the browser's default settings for interpreting how tags should be displayed, letting you use any HTML element indicated by an opening and closing tag (including the <p> tag) to apply style attributes defined either locally or in a stylesheet.
Stylesheets contain rules, composed of selectors and declarations that define how styles will be applied. The selector (a redefined HTML element, class name, or ID name) is the link between the HTML document and the style. There are two different kinds of selectors: types (HTML element tags) and attributes (such as class and ID names).
A CSS declaration has two parts,
a property ("color") and a value ("red").
The basic syntax of a rule
selector {property 1: value 1; property 2: value: 2} "
An example (containing two declarations, as above)
P {font-size: 8pt; color: red}
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Local, Global, and Linked Stylesheets
Local (inline) stylesheet declarations, specific to a single instance on a page, can be used instead of <font> tags to specify font size, color, and typeface and to define margins, leading, etc.
<p style="font size: small; color: red; font-weight: bold; font-family: Arial, Helvetica, non-serif">This is a local stylesheet declaration. </p>
Global (embedded) stylesheet declarations, applicable to an entire document, are defined within the <style> and </style> tags, which precede the <body> tag in the HTML document and are usually placed in the header.
To embed a global stylesheet in your HTML document:
<html>
<head>
<title>Title</title>
<style type="text/css">
<!--
[STYLE INFORMATION GOES HERE]
-->
</style>
</head>
<body>
[DOCUMENT BODY GOES HERE]
</body>
</html>
Linked stylesheet declarations use a single stylesheet (in a separate file, saved with the .css suffix) to define multiple pages. A typical .css file is a text file containing style rules, as here:
P {font-family: non-serif; font-size: medium; color: red}
H1 {font-family: serif; font-size: x-large; color: green}
H2 {font-family: serif; font-size: large; color: blue}
To apply a .css stylesheet ("style.css" in the example below) to an HTML page, a <link> tag is added to the page header:
<head>
<link rel="stylesheet" href="style.css" type="text/css">
</head>
Inheritance
In cases where local, global, and linked style definitions conflict, the most specific stylesheet will generally take precedence: local overrides global, global overrides linked. Similarly, inline style attributes override ID, ID overrides class, and class overrides stylesheet-defined HTML elements.
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Font Size and
Color
Font size may be defined in points, pixels, inches, or centimeters (pt, px, in, cm) or as a percentage.
<absolute-size> can be: xx-small, x-small, small, medium, large, x-large, xx-large.
<relative-size> can be: larger, smaller.
Percentage Units
<percentage> indicates a number followed by a % sign: 50%.
In the text-indent, margin, padding, and width properties, percentage values are relative to the width of the parent element.
In the font-size property, percentage values are relative to the font size of the parent element.
In <color> values, percentages can be used to express RGB values.
Color Units
<color> can represent either <color-name> or <rgb> values, as defined below:
<color-name> can be: aqua, black, blue, fuchsia, gray, green, lime, maroon, navy, olive, purple, red, silver, teal, white, yellow
<rgb> can be: #<hex><hex><hex> rgb(<number>, <number>, <number>) rgb(<percentage>,<percentage>,<percentage>) <hex> represents a hexidecimal value, <number> a decimal value, and <percentage> a percentage.
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Attributes
Class and ID
Classes let you create grouping schemes among styled HTML tags by adding the style definition of a particular class to the style definitions of several different tags. In the stylesheet, a class name is preceded by a period (.) to identify it as such:
.foo {property 1: value 1; property 2: value 2}
A very simple example:
<style>
P {font-family: sans-serif; font-size: 10pt}
H1 {font-family: serif; font-size: 30pt}
H2 {font-family: serif; font-size: 24pt}
.red {color: red}
.green {color: green}
.blue {color: blue}
</style>
The tags and classes can then be used in combination:
<h1 class="red">This is rendered as 30-point red serif text.</h1>
<p class="red">This is rendered as 10-point red sans-serif text.</p>
Or not:
<p>This is rendered as 10-point sans-serif text in the default color.</p>
The ID attribute is used for a uniquely defined style within a stylesheet. In the stylesheet, an ID name is preceded by a hash mark (#) to identify it as such:
#foo {property 1: value 1; property 2: value 2}
<h2 id="foo">Text rendered in the foo style.<h2>
Text-Level Attributes: <SPAN> and <DIV>
The <span> tag is generally used to apply a style to inline text:
<p><span class="foo">This text is rendered as foo-style</span> and this is not.
The <div> tag is generally used to apply a style to a block of text, which can also include other HTML elements:
<div class="foo">
<p>The "foo" style will be applied to this text, and to <a href="page.html">this text</a> as well.
</div>
The style attribute provides a way to define a style for a single instance of an element:
<p style="font-size: 10pt; color: red">This text is rendered as red, 10-point type</p>
The class, ID, and style attributed can be applied within the <span> and <div> elements. Used with class or ID, the <span> and <div> tags work like customized HTML tags, letting you define logical containers and apply a style to their contents.
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