Cascading Style Sheets, fondly referred to as CSS, is a simple design language intended to simplify
the process of making web pages presentable.
CSS handles the look and feel part of a web page. Using CSS, you can control the color of the text,
the style of fonts, the spacing between paragraphs, how columns are sized and laid out, what
background images or colors are used, layout designs,variations in display for different devices
and screen sizes as well as a variety of other effects.
CSS is easy to learn and understand but it provides powerful control over the presentation of an
HTML document. Most commonly, CSS is combined with the markup languages HTML or XHTML.
Advantages of CSS
CSS saves time − You can write CSS once and then reuse same sheet in multiple HTML
pages. You can define a style for each HTML element and apply it to as many Web pages as
you want.
Pages load faster − If you are using CSS, you do not need to write HTML tag attributes
every time. Just write one CSS rule of a tag and apply it to all the occurrences of that tag. So
less code means faster download times.
Easy maintenance − To make a global change, simply change the style, and all elements in
all the web pages will be updated automatically.
Superior styles to HTML − CSS has a much wider array of attributes than HTML, so you
can give a far better look to your HTML page in comparison to HTML attributes.
Multiple Device Compatibility − Style sheets allow content to be optimized for more than
one type of device. By using the same HTML document, different versions of a website can
be presented for handheld devices such as PDAs and cell phones or for printing.
Global web standards − Now HTML attributes are being deprecated and it is being
recommended to use CSS. So its a good idea to start using CSS in all the HTML pages to
make them compatible to future browsers.
Offline Browsing − CSS can store web applications locally with the help of an offline
catche.Using of this, we can view offline websites.The cache also ensures faster loading and
better overall performance of the website.
Platform Independence − The Script offer consistent platform independence and can
support latest browsers as well.
Who Creates and Maintains CSS?
CSS was invited by Håkon Wium Lie on October 10, 1994 and maintained through a group of
people within the W3C called the CSS Working Group. The CSS Working Group creates documents
called specifications. When a specification has been discussed and officially ratified by W3C
members, it becomes a recommendation.
These ratified specifications are called recommendations because the W3C has no control over
the actual implementation of the language. Independent companies and organizations create that
software.
NOTE − The World Wide Web Consortium, or W3C is a group that makes recommendations about
how the Internet works and how it should evolve.
CSS Versions
Cascading Style Sheets, level 1 CSS1 was came out of W3C as a recommendation in December
1996. This version describes the CSS language as well as a simple visual formatting model for all
the HTML tags.
CSS2 was became a W3C recommendation in May 1998 and builds on CSS1. This version adds
support for media-specific style sheets e.g. printers and aural devices, downloadable fonts,
element positioning and tables.
CSS3 was became a W3C recommendation in June 1999 and builds on older versions CSS. it has
divided into documentations is called as Modules and here each module having new extension
features defined in CSS2.
CSS3 Modules
CSS3 Modules are having old CSS specifications as well as extension features.
Selectors
Box Model
Backgrounds and Borders
Image Values and Replaced Content
Text Effects
2D/3D Transformations
Animations
Multiple Column Layout
User Interface
CCSSSS -- SSYYNNTTAAXX
A CSS comprises of style rules that are interpreted by the browser and then applied to the
corresponding elements in your document. A style rule is made of three parts −
Selector − A selector is an HTML tag at which a style will be applied. This could be any tag
like <h1> or <table> etc.
Property - A property is a type of attribute of HTML tag. Put simply, all the HTML attributes
are converted into CSS properties. They could be color, border etc.
Value - Values are assigned to properties. For example, color property can have value either
red or #F1F1F1 etc.
You can put CSS Style Rule Syntax as follows −
selector { property: value }
Example: You can define a table border as follows −
table{ border :1px solid #C00; }
Here table is a selector and border is a property and given value 1px solid #C00 is the value of
that property.
You can define selectors in various simple ways based on your comfort. Let me put these selectors
one by one.
The Type Selectors
This is the same selector we have seen above. Again, one more example to give a color to all level
1 headings:
h1 {
color: #36CFFF;
}
The Universal Selectors
Rather than selecting elements of a specific type, the universal selector quite simply matches the
name of any element type −
* {
color: #000000;
}
This rule renders the content of every element in our document in black.
The Descendant Selectors
Suppose you want to apply a style rule to a particular element only when it lies inside a particular
element. As given in the following example, style rule will apply to <em> element only when it lies
inside <ul> tag.
ul em {
color: #000000;
}
The Class Selectors
You can define style rules based on the class attribute of the elements. All the elements having
that class will be formatted according to the defined rule.
.black {
color: #000000;
}
This rule renders the content in black for every element with class attribute set to black in our
document. You can make it a bit more particular. For example:
h1.black {
color: #000000;
}
This rule renders the content in black for only <h1> elements with class attribute set to black.
You can apply more than one class selectors to given element. Consider the following example:
<p >
This para will be styled by the classes center and bold.
</p>
The ID Selectors
You can define style rules based on the id attribute of the elements. All the elements having that id
will be formatted according to the defined rule.
#black {
color: #000000;
}
This rule renders the content in black for every element with id attribute set to black in our
document. You can make it a bit more particular. For example −
h1#black {
color: #000000;
}
This rule renders the content in black for only <h1> elements with id attribute set to black.
The true power of id selectors is when they are used as the foundation for descendant selectors,
For example:
#black h2 {
color: #000000;
}
In this example all level 2 headings will be displayed in black color when those headings will lie
with in tags having id attribute set to black.
The Child Selectors
You have seen the descendant selectors. There is one more type of selector, which is very similar
to descendants but have different functionality. Consider the following example −
body > p {
color: #000000;
}
This rule will render all the paragraphs in black if they are direct child of <body> element. Other
paragraphs put inside other elements like <div> or <td> would not have any effect of this rule.
The Attribute Selectors
You can also apply styles to HTML elements with particular attributes. The style rule below will
match all the input elements having a type attribute with a value of text −
input[type = "text"]{
color: #000000;
}
The advantage to this method is that the <input type = "submit" /> element is unaffected, and the
color applied only to the desired text fields.
There are following rules applied to attribute selector.
p[lang] − Selects all paragraph elements with a lang attribute.
p[lang="fr"] − Selects all paragraph elements whose lang attribute has a value of exactly
"fr".
p[lang~="fr"] − Selects all paragraph elements whose lang attribute contains the word "fr".
p[lang|="en"] − Selects all paragraph elements whose lang attribute contains values that
are exactly "en", or begin with "en-".
Multiple Style Rules
You may need to define multiple style rules for a single element. You can define these rules to
combine multiple properties and corresponding values into a single block as defined in the
following example −
h1 {
color: #36C;
font-weight: norm al;
letter-spacing: .4em ;
m argin-bottom : 1em ;
text-transform : lowercase;
}
Here all the property and value pairs are separated by a semi colon ; . You can keep them in a
single line or multiple lines. For better readability we keep them into separate lines.
For a while, don't bother about the properties mentioned in the above block. These properties will
be explained in the coming chapters and you can find complete detail about properties in CSS
References.
Grouping Selectors
You can apply a style to many selectors if you like. Just separate the selectors with a comma, as
given in the following example −
h1, h2, h3 {
color: #36C;
font-weight: norm al;
letter-spacing: .4em ;
m argin-bottom : 1em ;
text-transform : lowercase;
}
This define style rule will be applicable to h1, h2 and h3 element as well. The order of the list is
irrelevant. All the elements in the selector will have the corresponding declarations applied to
them.
You can combine the various class selectors together as shown below −
#content, #footer, #supplem ent {
position: absolute;
left: 510px;
width: 200px;
}
CCSSSS -- IINNCCLLUUSSIIONN
There are four ways to associate styles with your HTML document. Most commonly used methods
are inline CSS and External CSS.
Embedded CSS - The <style> Element
You can put your CSS rules into an HTML document using the <style> element. This tag is placed
inside <head>...</head> tags. Rules defined using this syntax will be applied to all the elements
available in the document. Here is the generic syntax −
Following is the example of embed CSS based on the above syntax −
<!DOCTYPE htm l>
<htm l>
<head>
<style type = "text/css" m edia = "all">
body {
background-color: linen;
}
h1 {
color: m aroon;
m argin-left: 40px;
}
</style>
</head>
<body>
<h1>This is a heading</h1>
<p>This is a paragraph.</p>
</body>
</htm l>
It will produce the following result −
Attributes
Attributes associated with <style> elements are −
Attribute Value Description
type text/css Specifies the style sheet language as a content-type MIMEtype. This is
required attribute.
media
screen
tty
tv
projection
handheld
print
braille
aural
all
Specifies the device the document will be displayed on. Default value
is all. This is an optional attribute.
Inline CSS - The style Attribute
You can use style attribute of any HTML element to define style rules. These rules will be applied to
that element only. Here is the generic syntax −
<elem ent style = "...style rules....">
Attributes
Attribute Value Description
style style rules The value of style attribute is a combination of style declarations
separated by semicolon ; .
Example
Following is the example of inline CSS based on the above syntax −
<htm l>
<head>
</head>
<body>
<h1 style = "color:#36C;"> This is inline CSS </h1>
</body>
</htm l>
It will produce the following result −
External CSS - The <link> Element
The <link> element can be used to include an external stylesheet file in your HTML document.
An external style sheet is a separate text file with .css extension. You define all the Style rules
within this text file and then you can include this file in any HTML document using <link> element.
Here is the generic syntax of including external CSS file −
<head>
<link type = "text/css" href = "..." m edia = "..." />
</head>
Attributes
Attributes associated with <style> elements are −
Attribute Value Description
type text/css Specifies the style sheet language as a content-type MIMEtype. This
attribute is required.
href URL Specifies the style sheet file having Style rules. This attribute is a
required.
media
screen
tty
tv
projection
handheld Specifies the device the document will be displayed on. Default value
is all. This is optional attribute.
print
braille
aural
all
Example
Consider a simple style sheet file with a name mystyle.css having the following rules −
h1, h2, h3 {
color: #36C;
font-weight: norm al;
letter-spacing: .4em ;
m argin-bottom : 1em ;
text-transform : lowercase;
}
Now you can include this file mystyle.css in any HTML document as follows −
<head>
<link type = "text/css" href = "m ystyle.css" m edia = " all" />
</head>
Imported CSS - @import Rule
@import is used to import an external stylesheet in a manner similar to the <link> element. Here
is the generic syntax of @import rule.
<head>
<@ im port "URL";
</head>
Here URL is the URL of the style sheet file having style rules. You can use another syntax as well −
<head>
<@ im port url("URL");
</head>
Example
Following is the example showing you how to import a style sheet file into HTML document −
<head>
@ im port "m ystyle.css";
</head>
CSS Rules Overriding
We have discussed four ways to include style sheet rules in a an HTML document. Here is the rule
to override any Style Sheet Rule.
Any inline style sheet takes highest priority. So, it will override any rule defined in
<style>...</style> tags or rules defined in any external style sheet file.
Any rule defined in <style>...</style> tags will override rules defined in any external style
sheet file.
Any rule defined in external style sheet file takes lowest priority, and rules defined in this file
will be applied only when above two rules are not applicable.
Handling old Browsers
There are still many old browsers who do not support CSS. So, we should take care while writing
our Embedded CSS in an HTML document. The following snippet shows how you can use comment
tags to hide CSS from older browsers −
<style type="text/css">
<!--
body, td {
color: blue;
}
-->
</style>
CSS Comments
Many times, you may need to put additional comments in your style sheet blocks. So, it is very easy
to comment any part in style sheet. You can simple put your comments inside /*.....this is a
comment in style sheet.....*/.
You can use /* ....*/ to comment multi-line blocks in similar way you do in C and C++ programming
languages.
Example
<!DOCTYPE htm l>
<htm l>
<head>
<style>
p {
color: red;
/* This is a single-line com m ent * /
text-align: center;
}
/* This is a m ulti-line com m ent * /
</style>
</head>
<body>
<p>Hello World!</p>
</body>
</htm l>
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