Stylesheets Guide Reference 1
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}
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.
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.
Units of Measure
Throughout this CSS reference guide, abstract values (notably values involving units of measure) appear between angle brackets: <color>. They should be replaced by actual values as indicated in the key below.
Length Units
<length> indicates a number followed by a unit of measure: 24px.
The number can be an integer or a decimal fraction, and can be preceded by + or -.
Units can be absolute or relative:
Absolute: mm, cm, in, pt, pc (millimeters, centimeters, inches, points, picas)
Relative: em, ex, px (the element’s font height, the element’s x-height, pixels)
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.