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
Styles Solved a Big Problem
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. It saves a lot of work.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!
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 attribute you want to change. Each property has a value.
A CSS declaration always ends with a semicolon, and declaration groups are surrounded by curly brackets:
Eg: p {color:red;text-align:center;}
CSS
Comments
A CSS comment begins with
"/*", and ends with "*/", like this:
/*This is a comment*/
p
{
text-align:center;
/*This is another comment*/
color:black;
font-family:arial;
}
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".
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":
Example
#para1
{
text-align:center;
color:red;
}
{
text-align:center;
color:red;
}
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:
Efg: .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:
p.center
{text-align:center;}
Three
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>
<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");}
p {margin-left:20px;}
body {background-image:url("images/back40.gif");}
Do
not add a space between the property value and the unit (such as margin-left:20
px). The correct way is: margin-left:20px
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>
<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. 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>
a)
CSS Background
CSS background properties are used
to define the background effects of an element.
CSS properties used for background effects:
- background-color
- background-image
- background-repeat
- background-attachment
- background-position
Background Color
eg:
body {background-color:#b0c4de;}
With
CSS, a color is most often specified by:
- a HEX value - like "#ff0000"
- an RGB value - like "rgb(255,0,0)"
- a color name - like "red"
Background Image
The background-image property specifies an image to use as
the background of an element. By default, the image is repeated so it covers
the entire element. The background image for a page can be set like this: body {background-image:url('paper.gif');}By default, the background-image property repeats an image both horizontally and vertically. If the image is repeated only horizontally (repeat-x), the background will look better:
body
{
background-image:url('gradient2.png');
background-repeat:repeat-x;
}
Showing the image only once is specified by the background-repeat property:
body
{
background-image:url('img_tree.png');
background-repeat:no-repeat;
}
{
background-image:url('img_tree.png');
background-repeat:no-repeat;
}
b)
CSS Text
=> Text Color
The color property is used to set the color of the text.body {color:blue;}
h1 {color:#00ff00;}
h2 {color:rgb(255,0,0);}
ð
Text
Alignment
The text-align property is used
to set the horizontal alignment of a text. Text can be centered, or aligned to
the left or right, or justified. When text-align is set to "justify",
each line is stretched so that every line has equal width, and the left and
right margins are straight (like in magazines and newspapers).
h1
{text-align:center;}p.date {text-align:right;}
p.main {text-align:justify;}
ð Text Decoration
The text-decoration property is used to set or remove
decorations from text.The text-decoration property is mostly used to remove underlines from links for design purposes: a {text-decoration:none;}
It can also be used to decorate
text:
h1{text-decoration:overline;}
h2{text-decoration:line-through;}
h3{text-decoration:underline;}
h4 {text-decoration:blink;}
h2{text-decoration:line-through;}
h3{text-decoration:underline;}
h4 {text-decoration:blink;}
ð Text
Transformation
The text-transform property is used to specify uppercase
and lowercase letters in a text. It can be used to turn everything into
uppercase or lowercase letters, or capitalize the first letter of each word.
p.uppercase
{text-transform:uppercase;}
p.lowercase {text-transform:lowercase;}
p.capitalize {text-transform:capitalize;}
p.lowercase {text-transform:lowercase;}
p.capitalize {text-transform:capitalize;}
ð Text-align Property
h1 {text-align:center}
h2 {text-align:left}
h3 {text-align:right}
c)
CSS Font
CSS font properties define the font family, boldness, size, and the style
of a text.
Difference Between Serif and
Sans-serif Fonts
CSS Font Families
In
CSS, there are two types of font family names:
- generic family - a group of font families with a similar look (like "Serif" or "Monospace")
- font family - a specific font family (like "Times New Roman" or "Arial")
Generic family
|
Font family
|
Description
|
Serif
|
Times New RomanGeorgia
|
Serif fonts have small lines at
the ends on some characters
|
Sans-serif
|
Arial
Verdana |
"Sans" means without -
these fonts do not have the lines at the ends of characters
|
Monospace
|
Courier New
Lucida Console |
All monospace characters have the
same width
|
Setting font family,style and
p{font-family:"Times New Roman", Times, serif;}
p.normal {font-style:normal;}
p.italic {font-style:italic;}
p.oblique {font-style:oblique;}
h1
{font-size:40px;}
h2 {font-size:30px;}
p {font-size:14px;}
h2 {font-size:30px;}
p {font-size:14px;}
d)
CSS Links
Styling Links
Links
can be styled with any CSS property (e.g. color, font-family, background,
etc.).Special for links are that they can be styled differently depending on
what state they are in.
The
four links states are:
- a:link - a normal, unvisited link
- a:visited - a link the user has visited
- a:hover - a link when the user mouses over it
- a:active - a link the moment it is clicked
a:link
{color:#FF0000;} /* unvisited link */
a:visited {color:#00FF00;} /* visited link */
a:hover {color:#FF00FF;} /* mouse over link */
a:active {color:#0000FF;} /* selected link */
a:visited {color:#00FF00;} /* visited link */
a:hover {color:#FF00FF;} /* mouse over link */
a:active {color:#0000FF;} /* selected link */
Background Color
The
background-color property specifies the background color for links:
Example
a:link {background-color:#B2FF99;}
a:visited {background-color:#FFFF85;}
a:hover {background-color:#FF704D;}
a:active {background-color:#FF704D;}
a:visited {background-color:#FFFF85;}
a:hover {background-color:#FF704D;}
a:active {background-color:#FF704D;}
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