CSS Introduction
Before your begin:
Before you begin, it's important that you know Windows or Unix. A working knowledge of Windows or Unix makes it much easier to learn HTML.You should be familiar with:
Basic word processing using any text editor.
How to create directories and files.
How to navigate through different directories.
Basic understanding on internet browsing using a browser like Internet Explorer or Firefox etc.
Basic understanding on developing simple Web Pages using HTML or XHTML.
If you are new to HTML and XHTML then I would suggest you to go through our HTML Tutorial or XHTML Tutorial. Anyone of HTML or XHTML is enough to proceed.
What is CSS?
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, 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:
- Superior styles to HTML - CSS has a much wider array of attributes than HTML so you can give far better look to your HTML page in comparison of 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.
- Who Creates and Maintains CSS?
- CSS is created 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.
- CSS Syntax – Selectors
- 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 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 or 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 1headings : h1 { color: #36CFFF; }
The Universal Selectors:
Rather than selecting elements of a specific type, the universal selector quite simply matches thename 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 class="center bold"> 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 only when those headings will lie with in tags having id attribute set to black.
The Child Selectors:
You have seen descendant selectors. There is one more type of selectors 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> etc. 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 input elements that has 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: normal; letter-spacing: .4em; margin-bottom: 1em; text-transform: lowercase; }
Here all the property and value pairs are separated by a semi colon (;). You can keep them in a ingle 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 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: normal; letter-spacing: .4em; margin-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 various class selectors together as shown below: #content, #footer, #supplement { position: absolute; left: 510px; width: 200px; }
CSS Inclusion - Associating Styles
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: <head> <style type="text/css" media="..."> Style Rules ............ </style> </head>
Attributes:
Attributes associated with <style> elements are: Attribute Value Description type text/css Specifies the style sheet language as a content-type (MIME type). 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 optional attribute.
Example:
Following is the example of embed CSS based on above syntax: <head> <style type="text/css" media="all"> h1{ color: #36C; } </style> </head>
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: <element 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 above syntax: <h1 style ="color:#36C;"> This is inline CSS </h1>
This will produce following result: This is inline CSS
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="..." media="..." /> </head>
Attributes:
Attributes associated with <style> elements are: Attribute Value Description type text/css Specifies the style sheet language as a content-type (MIME type). This attribute is required. href URL Specifies the style sheet file having Style rules. This attribute is a required. media screen tty tv projection Specifies the device the document will be displayed on. Default value is all. This is optional attribute.
Tip: In some rare situations, when the attribute value itself contains quotes, it is necessary to use single quotes: name='John "ShotGun" Nelson'