Difference between revisions of "Cascade Style Sheets"
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Revision as of 10:29, 19 May 2008
Cascade Style Sheets (CSS)
A CSS is made up of two parts: the selector and declaration. The selector states which tag the rule applies. The declaration stats what happens when the rule is applied.
The declaration is made up of two elements: a property and value. A declaration must end with a semicolon.
Multiple declarations can be contained in a single rule.
Multiple selectors can be contained in a single rule. A comma must be used after each selector except the last.
h1, h2, h3 {color:red; font-weight:bold;}
Multiple rules can be applied to the same selector.
h1, h2, h3 {color:red; font-weight:bold;}
h3 {font-style:italic;}
Selectors
Contextual Selectors
Contextual selectors use more than one tag in the selector. The tag closest to the declaration is the targeted tag. The additional tag(s) state where the target tag must be located in the markup up in order for target tag to be affected. Contextual selectors have spaces between them.
Example: The p is targeted tag. Only p tags within div tags will be red.
div p {color:red;}
Contextual selector examples
<html> <head> <title>Contextual Selector Example 1</title> <link href="style_sheets/contextual_selector_example_1.css" rel="stylesheet" type="text/css"> </head> <body>
Child selectors
Write a rule so the target tag has to be a child of a specific tag.
p>em {color:green;}
Contextual Class Selectors
You can combine tag and class name to make a selector more specific.
The second line states any tags with "specialtext" class will be bold.
The third line states "specialtext" class must be within the context of p tag for rule to apply.
p { font-family: Helvetica, sans-serif; }
.specialtext { font-weight:bold; }
p.specialtext { color:red}
You can further specify by adding more tags.
The fourth line states span tag within a paragraph with "specialtext" class will be italicized
p { font-family: Helvetica, sans-serif; }
.specialtext { font-weight:bold; }
p.specialtext { color:red}
p.specialtext span { font-style:italic; }
Skipping the restrictions of hierarchy
The line states span tag can be a descendant of any tag with specialtext class
.specialtext span { color:blue; }
IDs
ID synax is similar to classes except a hash (#) symbol is used versus a class's period.
Difference between Classes & IDs
The ID can only be used once per page and a class may appear many times.
If you want to identify a unique piece of your page's markup use an ID.
If you want to apply rules to multiple tags in same page or many pages use a class.
Universal Selector
The asterisk (*) means anything so this rule means all text will be blue.
* { color:blue; }
Another use is as the inverse of a child selector. This rule means any em tag that is at least a grandchild of the p tag, but not a child, is selected.
p * em { font-weight:bold; }
Adjacent Sibling Selector
Rule selects a tag that follows a specific sibling tag. p48
Attribute Selector
Attribute selectors use the attributes of the tag. p48
Adding Styles to Web pages
Three ways to add styles to your pages.
Inline
Add to a tag using style attribute
<p style="enter CSS"></p>
Embedded
Add styles in the head of XHTML document
<style type="text/css">enter CSS</style>
Linked
Style is in another document and the markup is linked to the style.
<link href="style_sheet.css" media="screen" rel="stylesheet" type="text/CSS" />
Pseudo Classes
Classes that cause rules to be applied when a specific event happens. These classes are not attached to tags in markup. p50
Anchor Link Pseudo Classes
Commonly used with hyperlinks. p50
Link Visited Hover Active
Other Useful Pseudo-Classes
This rule selects the first-child element with the name x.
x:first-child
This rule selects the focus of the user with the name x.
x:focus
Pseudo-elements
Provides the effect of extra markup without the markup in your code.
This rule selects the first letter of tag name x and applies your style.
x:first-letter
This rule selects the first line of tag name x and applies your style.
x:first-line
This rule adds specified text before an element of tag name x.
x:before
This rule adds specified text after an element of tag name x.
x:after
Example of x:before and x:after
h1.age:before {content:"Age:"}
h1.age:after {content:"years old."}
Code <h1 class="age">36</h1> displays "Age: 36 years old."
Cascade
Styles passing from higher to lower hierarchy levels.
Cascade Rules
Cascade Rule 1 : Find all declarations that apply to each element and property
Cascade Rule 2 : Sort by order and weight
Weight of declaration
Define a rule as important using the exclamation point. Marking a tag as important will override the cascade.
p {color:red !important; font-size:12pt;}