Cascade Style Sheets
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;}
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.
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>
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; }
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" />