introduction to css cascading style sheets

What is CSS
• Cascading Style Sheets
• Contains the rules for the presentation of
HTML.
+ =
HTML CSS Web Page
• CSS was introduced to keep the
presentation information separate from
HTML markup (content).

Before CSS
• Initially Designers used presentation tags like (FONT, B, BR, TABLE
etc.) and spacers GIFs to control the design of web pages.

• Any modification in the design of websites
was a very difficult and boring task , as it
evolves manually editing every HTML
page.

Providing support for multiple browsers was a
difficult task.

Sources of Styles
Author (developer) Styles
• Inline Styles - As inline attribute “style” inside HTML tags
<div style=“font-weight: bold;”>I am bold</div>
• Embedded Styles - As embedded style tag with in HTML
document.
<html>
<head>
<title>Welcome to Vendio!</title>
<style>
.footer {
width:90%;
}
</style>
-------
</html>
• Linked Styles - Inside separate files with .css extension
<link rel="stylesheet" href=“external.css" type="text/css" />

Sources of Styles(contd.)
• User Style sheets
This file contains the user created styles .
[firefox profile folder]/ chrome/userContent-example.css
is the current user’s style sheet file for the firefox.
• Browser default style sheet
This file contains default styles for all users of a
browser
[firefox folder]/res/html.css is the default style sheet
file for the firefox.

CSS Selectors
• ID based ( #)
HTML CSS
<div id=“content”> #content {
Text width: 200px;
</div> }
ID selectors should be used with single elements.

Class based selector
• Class (.)
HTML CSS
<div class=“big”> .big{
Text width: 200px;
</div> }
<div>
<span class=“big”>some text </span>
</div>
Class based styles can be used by multiple HTML elements.

Tag based selectors
• Tag (Tag name)
HTML CSS
<div> DIV {
Text width: 200px;
</div> }
<div> SPAN {
<span>some text </span> font-size:130%;
</div> }
<span>some other text </span>

Grouping
• Multiple selectors can be grouped in a
single style declaration by using , .
H1, P , .main {
font-weight:bold;
}

Descendant selectors
Descendant selectors are used to select elements that
are descendants (not necessarily children) of another
element in the document tree.
HTML CSS
<div class=“abc”> DIV.abc P {
<div> font-weight:bold;
<P> }
Hello there!
</p>
</div>
</div>

Child selectors
A child selector is used to select an element that is a
direct child of another element (parent). Child selectors
will not select all descendants, only direct children.
HTML CSS
<div > DIV.abc > P {
<div class=“abc”> font-weight:bold;
<P> }
Hello there!
</p>
</div>
</div>

Universal selectors
Universal selectors are used to select any
element.
* {
color: blue;
}

Adjacent sibling selectors
Adjacent sibling selectors will select the
sibling immediately following an element.
DIV.abc + P {
font-weight: bold;
}
will work for
<div>
<div class=“abc”>Message</div>
<P>Hello there!</p>
</div>

Attribute selectors
Attribute selectors selects elements based
upon the attributes present in the HTML
Tags and their value.
IMG[src="small.gif"] {
border: 1px solid #000;
}
will work for
<img src=“small.gif” />

CSS Pseudo-classes
selector:pseudo-class { property: value }
:link
:visited } Link (A tag) related pseudo classes
:hover
:active
:after
:before
:first-child
:focus
:first-letter
:first-line
:lang

CSS Values
• Words: text-align:center;.
• Numerical values: Numerical values are usually
followed by a unit type.
font-size:12px;
12 is the numerical value and px is the unit type pixels.
– Absolute Values – in, pc, px, cm, mm, pt
– Relative Values – em, ex, %
• Color values: color:#336699 or color#369 or
rgb(255, 255, 255).

Categories of CSS properties
• Positioning and layout handling related.
• Background related properties.
• Font and text related
• Links related.
• Lists related.
• Table related.

Cascade
The CSS cascade assigns a weight
to each style rule. When several
rules apply, the one with the
greatest weight takes precedence.
Order of preference for various
styles:
– Default browser style sheet
(weakest)
– User style sheet
– Author style sheet
– Author embedded styles
– Author inline styles (strongest)

CSS Specificity
Rule 1. CSS File >> Embedded >> Inline
Rule 2. TAG >> class >> ID

Inheritance
• Styles that relate to text and appearance
are inherited by the descendant
elements.
• Styles that relate to the appearance of
boxes created by styling DIVs,
paragraphs, and other elements, such as
borders, padding, margins are not
inherited.

Refrences
• www.w3schools.com
• www.w3.org
• World wide web

introduction to css cascading style sheets

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