css-cascading style sheets - introduction

CSSCASCADING STYLE SHEETS

Mukesh N. TekwaniComputer Science & [email protected]. Y. College, Mumbai, India

mailto:[email protected]

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Prof. Mukesh N. Tekwani

WHAT IS CSS? CSS stands for Cascading Style Sheets CSS defines HOW to display HTML elements Styles are normally stored in Style Sheets External Style Sheets can save you a lot of work External Style Sheets are stored in CSS files Multiple style definitions will cascade into one CSS selects an element and sets the rules for

that element. These set of rules are known as style sheets and can be in the HEAD section of an HTML document or in an external style sheet.

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CSS RULES A CSS rule has 2 parts: a selector, and one or more

declarations:

Selector DeclarationH1 {color:blue; font-size:12px;)Here, color is the property and blue is the value of that property.

The selector is the HTML element that we want to style. The property is the attribute we want to change. Each attribute has a value.

CSS property names are separated by dashes when they are multiple words—for example, font-face, font-size, line-height, and so on.

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WHAT IS THE NEED FOR CSS? (OR WHAT ARE THE ADVANTAGES OF CSS?) HTML pages use a lot of markup to style the

pages.

There can be very complex structures of tables, nested frames, invisible pixel images for layout, etc.

This makes HTML page difficult to render for the browser.

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WHAT IS THE NEED FOR CSS? (OR WHAT ARE THE ADVANTAGES OF CSS?) Code: CSS is the standard for coding in HTML. CSS is compatible

with most browsers. CSS reduces the length of the codes of web page, which decreases the page size, making it easy and fast to load in browsers

Design: Use of CSS makes the design simple. CSS makes the management of the entire website easy to maintain by just changing the CSS file which contains the style details.

Bandwidth: CSS reduces the HTML coding and page size. This reduces the bandwidth usage.

Consistency: It is easy to maintain, handle and control the whole website made on CSS based HTML. Ex: Suppose we want to change the background of the entire website, we just need to change the background of the single page in the style sheet and the background of the whole website will change.

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WHAT IS MEANT BY STYLE RULES? A style rule is used to change the default

behavior of an HTML element. All style rules are contained in the <STYLE> element and this is put in the HEAD section of an HTML document.

A style rule is made up of 2 parts: a selector and a declaration. The selector determines the element to which the style is to be applied. The declaration gives the exact property values.

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WHAT IS MEANT BY STYLE RULES? Consider the <P> element. We can create a style rule for

this <P> element so that all paragraphs are in blue color and have a font size of 24px. The style rule is as follows:

<STYLE>P {COLOR:BLUE; FONT-SIZE:24px}

</STYLE> Consider the <H1> element. We can create a style for

this element so that all H1 headings are in red color. <STYLE TYPE = “TEXT/CSS”>

H1 {COLOR:RED} </STYLE>

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DEFINING THE STYLE FOR A SINGLE ELEMENT: We can define the style for a single element

as follows:

<H1 STYLE =”COLOR:BLUE”>This is a heading</H1>

This direct use of CSS is called inline style and is not recommended due to the tight coupling between the HTML document and the style.

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TRY… Write a style rule so that every <H1>

element on your web site is in green color and centered.

H1 {COLOR:GREEN; TEXT-ALIGN:CENTER}

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EXTERNAL STYLE SHEET: Placing style sheets in an external document

lets you specify rules for different HTML documents. An external style sheet is a text document with the file name extension of .CSS. This external style sheet contains the style rules for various elements.

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EXTERNAL STYLE SHEET:/* stylesheet 1 */H1 {COLOR:GREEN}H2 {COLOR:GREEN; BORDER:SOLID BLUE}(Other option for SOLID is DOTTED)The CSS line begins with a comment. The CSS style sheet does not contain any HTML code.

To link this external style sheet to an HTML document, we add the <LINK> element in the HEAD section of an HTML document:

<HEAD><TITLE>Sample document</TITLE><LINK HREF = “style1.css” REL = “stylesheet”></HEAD>

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EXTERNAL STYLE SHEET: The HTML file containing this code displays with

the characteristics given in the style sheet.

The HREF attribute gives the URL of the stylesheet. The REL attribute specifies the relationship between the linked and the current document.

The major advantage of external style sheets is that the styles can apply to all the web pages on a site. In order to make global changes, we just have to modify the external style sheet.

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DIFFERENT CSS SELECTION TECHNIQUES Selecting Multiple Elements:

By using multiple selectors, we can use less code. E.g., to make both <H1> and <H2> headings green, we can use the following rules:

<STYLE TYPE = “TEXT/CSS”><H1> {COLOR:GREEN}<H2> {COLOR:GREEN}</STYLE>

These two rules can be expressed in a single rule statement using multiple selectors for the same property as follows:

<STYLE TYPE = “TEXT/CSS”>H1, H2 {COLOR:GREEN}</STYLE>

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DIFFERENT CSS SELECTION TECHNIQUES Selecting by Context:

A context-based selector lets you specify the exact context in which a style is applied.

For example, to specify that the <I> elements appear in blue color only within the <H1> elements, we create the style rule as follows:<STYLE TYPE = “TEXT/CSS”>H1 I {COLOR:BLUE}</STYLE>

Note: We should not place a comma between the element H1 and I in the above example. Otherwise it will turn a contextual selection into a multiple element selection and blue color text will apply to both H1 headings and Italic text.

So don’t write this: H1 , I {COLOR:BLUE}

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DIFFERENT CSS SELECTION TECHNIQUES Selecting with the CLASS attribute:

The CLASS attribute lets you write rules and then apply them to groups of elements. Basically the CLASS attribute lets you define your own tags and apply them wherever you want.

To create a class, we first declare it within the <STYLE> element. The period (.) flag character indicates that the selector is a class selector.

<STYLE TYPE = “TEXT/CSS”>

.QUOTE {COLOR:RED}</STYLE>

Applying this style to a paragraph:<P CLASS=”QUOTE”> This is a paragraph </P>

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WHAT ARE THE CSS FONT PROPERTIES?

The following font properties can be controlled with CSS:

Font families and alternatesFont sizeFont weightLine heightLetter spacingText indentColor

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Example 1: Create a style rule that specifies Arial as the font for the <P> element.

<STYLE TYPE=”TEXT/CSS”>P {FONT-FAMILY:ARIAL}

</STYLE>

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Example 2: Create a style rule that specifies Arial as the font for the <P> element. In case Arial font is not available, use the Helvetica font.

<STYLE TYPE=”TEXT/CSS”>P {FONT-FAMILY:ARIAL, HELVETICA}</STYLE>

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Example 3: Create a style rule that specifies Arial as the font for the <P> element. In case Arial font is not available, use the Helvetica font. In case this too is not available, use a generic font like sans-serif.

<STYLE TYPE=”TEXT/CSS”>P {FONT-FAMILY:ARIAL, HELVETICA, SANS-SERIF}</STYLE>

The generic names we can use are: Monospace, Serif and Sans-serif.

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WHAT ARE THE CSS FONT PROPERTIES?Specifying Text Background Color:

Example 4: We can set the text background color (i.e., the color behind the text) for any element, by using the BACKGROUND-COLOR property, as follows:

<STYLE TYPE=”TEXT/CSS”>H2 {COLOR:WHITE; BACKGROUND-COLOR:BLUE}</STYLE>

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WHAT IS THE CLASS SELECTOR IN CSS? The CLASS attribute lets you write rules and then apply them to

groups of elements. The CLASS attribute lets you define your own tags and apply

them wherever you want.

To create a class, we first declare it within the <STYLE> element. The period (.) flag character indicates that the selector is a class selector.

<STYLE TYPE = “TEXT/CSS”>.QUOTE {COLOR:RED}</STYLE>

Applying this style to a paragraph:<P CLASS=”QUOTE”> This is a paragraph </P>

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WHAT IS THE CLASS SELECTOR IN CSS?

Example 2: Create a class rule called “veryimportant” that sets the background color to yellow. Apply this to a H1 heading and two paragraphs. Also show how a para is rendered if the class is not applied to it.

<HTML><HEAD><STYLE TYPE="TEXT/CSS">.veryimportant {background-color: yellow;}</STYLE></HEAD><BODY><H1 CLASS="veryimportant">Example</h1><P CLASS="veryimportant">This is the first paragraph.</P><P>This is the second paragraph.</P><P Class="veryimportant">This is the third paragraph.</P></BODY></HTML>

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HOW TO SPECIFY TEXT MARGINS N CSS?

The MARGIN attribute is used to set the text margin on all four sides. We can also set the margins on individual sides with following settings:

MARGIN-TOPMARGIN-BOTTOMMARGIN-LEFTMARGIN-RIGHT

Example: Set the margin on all sides to 30 px<STYLE TYPE = “TEXT/CSS”>P {margin:30px}</STYLE>

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HOW TO SPECIFY THE TEXT BORDERS?

The BORDER property can be used to set the border style, color and width.

Syntax: {BORDER BORDER-STYLE BORDER-WIDTH BORDER-

COLOR}

Example<STYLE TYPE = “TEXT/CSS”>

P {BORDER: SOLID 2pt BLUE}</STYLE>

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CHANGING BACKGROUND COLOR WITH CSS<html><head><style type="text/css">body{

background-color:#b0c45e;}</style></head><body>

<h1>My CSS web page!</h1><p>Hello world!</p>

</body></html>

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SET AN IMAGE AS THE BACKGROUND OF A PAGE<html><head><style type="text/css">

body {background-image:url('paper.gif');}</style></head><body><h1>Hello World!</h1></body></html>

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EXAMPLECreate a style rule as follows: To display the date in

a right-aligned paragraph. To display the main text in a justified paragraph.

<html><head><style type="text/css">

h1 {text-align:center;}p.date {text-align:right;}p.main {text-align:justify;}

</style></head>

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EXAMPLE (CONTD)<body>

<h1>CSS text-align Example</h1><p class="date">Nov 2010</p><p class="main">This is the main paragraph in which text alignment is “justified”</p>

</body></html>

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EXAMPLECreate style rules for the four states of a link. <html><head><style type="text/css">

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 */

</style></head>

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EXAMPLE (CONTD)<body>

<p><b><a href="default.asp" target="_blank">This is a link</a></b></p>

</body></html>

Note: a:hover MUST come after a:link and a:visited in the CSS definition in order to be effective.a:active MUST come after a:hover in the CSS definition in order to be effective.

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EXAMPLE Create a style rule for H1 element with

following specifications:H1 tag with Background image: swirlbkg.jpgColor—greenLetter-spacing-7ptText-align- centerText-decoration-underlineText-transform--uppercase;Word-spacing: 2pt

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EXAMPLE(CONTD)H1 {

color:green;letter-spacing:7pt;text-align: center; text-decoration:underline; text-transform:uppercase; word-spacing: 2pt

}

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EXAMPLE Create a style rule for P tag with

following specifications:Color – magentafont-family – Algerianfont-size – mediumfont-style—italic font-weight—lighter

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EXAMPLEP{

color: magenta;font-family:Algerian;font-size: medium;font-style:italic;font-weight:-lighter;

}

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EXAMPLE TO ILLUSTRATE THE VARIOUS STYLES APPLIED TO LISTS:<html><head><style type="text/css">

ul.a {list-style-type:circle;} /* open circle */ul.b {list-style-type:square;} /* filled square */ul.e {list-style-type:disc;} /* filled circle */ol.c {list-style-type:upper-roman;} /* upper roman I */ol.d {list-style-type:lower-alpha;} /* lower alpha: a */

</style></head>

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LISTS<body><p>Example of unordered lists:</p>

<ul class="a"> <li>Coffee</li> <li>Tea</li> <li>Coca Cola</li>

</ul> <ul class="b">

<li>Coffee</li> <li>Tea</li> <li>Coca Cola</li>

</ul>

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LISTS<ul class="e"> <li>Coffee</li> <li>Tea</li> <li>Coca Cola</li></ul>

<p>Example of ordered lists:</p><ol class="c"> <li>Coffee</li> <li>Tea</li> <li>Coca Cola</li></ol>

</body></html>

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HANGING INDENTWrite a style rule for a <P> element with a 24 pt hanging indent and a 30 pixel margin on left and right sides.

<STYLE TYPE = "TEXT/CSS">P {

text-indent:-24pt;margin-left:30px;margin-right:30px

}</STYLE>

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ALIGNING TEXT WITH CSS<html><head><style>h1 {text-align:center;}p.date {text-align:right;}p.main {text-align:justify;}</style></head><body><h1>CSS text-align Example</h1><p class="date">May, 2009</p><p class="main">In my younger and more vulnerable years my father

gave me some advice that I've been turning over in my mind ever since. 'Whenever you feel like criticizing anyone,' he told me, just remember that all the people in this world haven't had the advantages that you've had.'</p>

<p><b>Note:</b> Resize the browser window to see how the value "justify" works.</p></body></html>

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QUESTIONS ? Read. Practice. Read. Practice. : : :

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css-cascading style sheets - introduction

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