Cascading Style Sheet
Contents
1.1 What is CSS? 1
1.2 CSS Comments 3
1.3 Three Ways to Insert CSS 4
1.4 Multiple Style Sheets 5
1.5 CSS Properties used for Background Effects 6
1.6 Text 9
1.7 CSS Font Families 10
1.8 CSS Links 13
1.9 CSS Lists 14
1.10 Table Borders 16
1.11 The CSS Box Model 18
1.12 CSS Padding 24
Cascading Style Sheets (CSS)
1.1 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
1.1.1 Styles
HTML was never intended to contain tags for formatting a document. HTML was intended to define the
content of a document, like:
<h1>This is a heading</h1>
<p>This is a paragraph.</p>
When tags like <font>, and color attributes were added to the HTML 3.2 specification, it started a
nightmare for web developers. Development of large web sites, where fonts and color information were added to every single page, became a long and expensive process.
To solve this problem, the World Wide Web Consortium (W3C) created CSS. In HTML 4.0, all
formatting could be removed from the HTML document, and stored in a separate CSS file.
All browsers support CSS today. CSS defines HOW HTML elements are to be displayed. Styles are normally saved in external .css files. External style sheets enable you to change the appearance and layout of all the pages in a Web site, just by editing one single file!
1.1.2 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 p to property and a value. The property is the style attribute you want to change. Each property has a value.
1.1.3 CSS Example
A CSS declaration always ends with a semicolon, and declaration groups are surrounded by curly
brackets:
p {color:red;text-align:center;}
To make the CSS more readable, you can put one declaration on each line, like this:
p
{
color:red;
text-align:center;
}
Example 1
<html>
<head>
<style type="text/css">
body {background-color:yellow;}
h1 {font-size:36pt;}
h2 {color:blue;}
p {margin-left:50px;}
</style>
</head>
<body>
<h1>This header is 36 pt</h1>
<h2>This header is blue and background is yellow </h2>
<p>This paragraph has a left margin of 50 pixels</p>
</body>
</html>
Output:
1.2 CSS Comments
Comments are used to explain your code, and may help you when you edit the source code at a later date.
Comments are ignored by browsers. A CSS comment begins with "/*", and ends with "*/".
/*This is a comment*/
p
{
text-align:center;
/*This is another comment*/
color:black;
font-family:arial;
}
1.2.1 The id and class Selectors
In addition to setting a style for a HTML element, CSS allows you to specify your own selectors called
"id" and "class".
1.2.1.1 The id Selector
The id selector is used to specify a style for a single, unique element. The id selector uses the id attribute
of the HTML element, and is defined with a "#". The style rule below will be applied to the element with
id="para1": Do not start an ID name with a number. It will not work in Mozilla/Firefox.
#para1
{
text-align:center;
color:red;
}
1.2.1.3 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 "." In the example below, all HTML elements with class="center" will be center-aligned: .center {text-align:center;}
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: Do NOT start a class name with a
number! This is only supported in Internet Explorer.
p.center {text-align:center;}
1.3 Three Ways to Insert CSS
There are three ways of inserting a style sheet:
External style sheet
Internal style sheet
Inline style
1.3.1 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");}
Do not leave spaces between the property value and the unit (such as margin-left:20 px). Correct way:
margin-left:20px
1.3.2 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>
1.3.3 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>
1.4 Multiple Style Sheets
If some properties have been set for the same selector in different style sheets, the values will be inherited from the more specific style sheet.
For example, an external style sheet has these properties for the h3 selector:
h3
{
color:red;
text-align:left;
font-size:8pt;
}
And an internal style sheet has these properties for the h3 selector:
h3
{
text-align:right;
font-size:20pt;
}
If the page with the internal style sheet also links to the external style sheet the properties for h3 will be:
color:red;
text-align:right;
font-size:20pt;
The color is inherited from the external style sheet and the text-alignment and the font-size is replaced by the internal style sheet.
1.4.1 Multiple Styles - Cascade into One
Styles can be specified:
inside an HTML element
inside the head section of an HTML page
in an external CSS file
Even multiple external style sheets can be referenced inside a single HTML document.
Cascading order What style will be used when there is more than one style specified for an HTML element?
Generally speaking we can say that all the styles will "cascade" into a new "virtual" style sheet by the following rules, where number four has the highest priority:
Browser default
External style sheet
Internal style sheet (in the head section)
Inline style (inside an HTML element)
So, an inline style (inside an HTML element) has the highest priority, which means that it will override a style defined inside the <head> tag, or in an external style sheet, or in a browser (a default value).
If the link to the external style sheet is placed after the internal style sheet in HTML <head>, the external style sheet will override the internal style sheet.
1.5 CSS properties used for background effects:
CSS background properties are used to define the background effects of an element.
background-color
background-image
background-repeat
background-attachment
background-position
Background Color
The background-color property specifies the background color of an element.
The background color of a page is defined in the body selector:
Example
