Introduction to CSS

WEB DESIGN TRAINING 03
INTRODUCTION TO CASCADING
STYLE SHEETS(CSS)
Presented by Folasade Adedeji

Cascading Style Sheets
 A key tool in web design
 CSS is the sister technology to HTML that is
used to style web pages.
 CSS is used to control the style and layout of
multiple Web pages all at once.
 CSS defines HOW HTML elements are to be
displayed.

Cascading Style Sheets
 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:

CSS Syntax
 A CSS declaration always ends with a
semicolon, and declaration groups are
surrounded by curly brackets:
 p {color:red;text-align:center;}
p
{
color:red;
text-align:center;
}

CSS Comment
 Comments are used to explain your code
 Comments are ignored by browsers.
 A CSS comment begins with "/*“
 and ends with "*/", for example:
/*This is a comment*/
p
{
text-align:center;
/*This is another comment*/
color:black;
font-family:arial;
}

CSS id and class
 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":
#para1
{
text-align:center;
color:red;
}

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:
Example
.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:
Example
p.center {text-align:center;}

How to Insert CSS
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 used 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/background.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>
hr {color:sienna;}
p {margin-left:20px;}
body {background-image:url("images/back.gif");}
</style>
</head>

Inline Styles
 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>

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.

Multiple Style Sheets
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.

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).

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
 The background-color property specifies the
background color of an element.
 The background color of a page is defined in
the body selector:
 Example
 body {background-color:#b0c4de;}

<!DOCTYPE html>
<html>
<head>
<style>
h1
{
background-color:#6495ed;
}
p
{
background-color:#e0ffff;
}
div
{
background-color:#b0c4de;
}
</style>
</head>
<body>
<h1>CSS background-color example!</h1>
<div>
This is a text inside a div element.
<p>This paragraph has its own background color.</p>
We are still in the div element.
</div>
</body>

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:
 Example
 body {background-image:url("paper.gif");}

Background Image - Repeat
Horizontally or Vertically
 By default, the background-image property
repeats an image both horizontally and
vertically.
 Some images should be repeated only
horizontally or vertically, or they will look
strange, like this:
 Example
 body
{
background-image:url(“back2.png");
}

 If the image is repeated only horizontally
(repeat-x), the background will look better:
 Example
 body
{
background-image:url(“back2.png");
background-repeat:repeat-x;
}

Background Image - Set position
and no-repeat
 Showing the image only once is specified by
the background-repeat property:
 Example
 body
{
background-image:url(“me.png");
background-repeat:no-repeat;
}

 In the example above, the background image is
shown in the same place as the text. We want to
change the position of the image, so that it does not
disturb the text too much.
 The position of the image is specified by the
background-position property:
 Example
 body
{
background-image:url(“me.png");
background-repeat:no-repeat;
background-position:right top;
}

Background - Shorthand
property
 As you can see from the examples above, there
are many properties to consider when dealing with
backgrounds.
 To shorten the code, it is also possible to specify
all the properties in one single property. This is
called a shorthand property.
 The shorthand property for background is simply
"background":
 Example
 body {background:#ffffff url(“me.png") no-repeat
right top;}

Introduction to CSS

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