What is CSS?
•CSS stands for Cascading Style Sheets
•Styles define how to display HTML elements
•Styles were added to HTML 4.0 to solve a problem
•External Style Sheets can save a lot of work
•External Style Sheets are stored in CSS files
CSS Syntax
A CSS rule has two main parts: a selector, and one or more declarations:
The selector is normally the HTML element you want to style.
Each declaration consists of a property and a value. The property is the style.
A CSS comment like this: /*This is a comment*/
The id Selector
The id selector defined with a "#" is used to specify a style for a unique element with id attribute i.e. id="para1".
| <html> <head> <style type="text/css"> #para1 { text-align:center; color:red; } </style> </head> <body> <p id="para1">Hello World!</p> <p>This paragraph is not affected by the style.</p> </body> </html> |
Tips: Do NOT start an ID name with a number! It will not work in Mozilla/Firefox.
The class Selector
The class selector is used to specify a style for a group of elements. Unlike the id selector, the class selector is most often used on several elements.
This allows you to set a particular style for many HTML elements with the same class.
The class selector uses the HTML class attribute, and is defined with a "."
| Example
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You can also specify that only specific HTML elements should be affected by a class.
In the example below, all p elements with class="center" will be center-aligned:
| Example
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Do NOT start a class name with a number! This is only supported in Internet ExplorerThree Ways to Insert CSS
There are three ways of inserting a style sheet:
- External style sheet
- Internal style sheet
- Inline style
External Style Sheet
An external style sheet is ideal when the style is applied to many pages. With an external style sheet, you can change the look of an entire Web site by changing one file. Each page must link to the style sheet using the <link> tag. The <link> tag goes inside the head section:
| < head> < link rel="stylesheet" type="text/css" href="mystyle.css" /> < /head> |
An external style sheet can be written in any text editor. The file should not contain any html tags. Your style sheet should be saved with a .css extension. An example of a style sheet file is shown below:
| hr {color:sienna;} p {margin-left:20px;} body {background-image:url("images/back40.gif");} |
Internal Style Sheet
An internal style sheet should be used when a single document has a unique style. You define internal styles in the head section of an HTML page, by using the <style> tag, like this:
| < head> < style type="text/css"> hr {color:sienna;} p {margin-left:20px;} body {background-image:url("images/back40.gif");} < /style> < /head> |
Inline Styles
An inline style loses many of the advantages of style sheets by mixing content with presentation. Use this method sparingly!
To use inline styles you use the style attribute in the relevant tag. The style attribute can contain any CSS property. The example shows how to change the color and the left margin of a paragraph:
| < p style="color:sienna;margin-left:20px">This is a paragraph.</p> |
Cascading order
Number 4 has the highest priority:
- Browser default
- External style sheet
- Internal style sheet (in the head section)
- Inline style (inside an HTML element)
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