Transcript Slides

Cascading Style Sheet (CSS)
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Cascading Style Sheets (CSS)
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a style defines the appearance of a document
element.
o E.g., font size, font color etc…
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a style sheet: collection of styles for a Web
page or Website
style sheets use common language and syntax
main style sheet standard: Cascading Style
Sheets (CSS)
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CSS history
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developed by WWW Consortium (www.w3c.org), the
same organization that develops standards for HTML
designed to augment HTML, not replace it
a whole new way of formatting Web pages
provides several tools not available with standard
HTML
different versions
o CSS1 released in 1996 (fonts, text, color, background)
o CSS2 released in 1998 (positioning, visual formatting)
o CSS3, latest standard being developed
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Benefits of style sheets
a design tool
 makes website design more flexible
 easier to maintain and modify
 more aesthetically interesting
 consistent look
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Applying a Style Sheet
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Three ways to apply a style to an HTML
document:
1. Inline Styles
2. Embedded Style Sheet
3. External Style Sheet
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Style types
o Inline styles
 styles are added to each tag within the HTML file
 style only affects that particular tag
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Using inline styles
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format a single section, better use inline style
syntax
<tag style=“style declarations”>
o tag is the name of an HTML element (h1, h2, p, etc)
o style declarations
the styles defined for the particular tag
 must be enclosed within double quotation marks
 use semi-colon separate multiple attributes
<tag style=“attribute1:value1; attribute:value2”>
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o e.g.
<h1 style="text-align: center; color: red">
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But what if there are same tags appearing
multiple times in the webpage and you want
to format all of them uniformly
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Style types (contd.)
o Inline styles
 styles are added to each tag within the HTML file
 style only affects that particular tag
o Embedded or global styles
 applied to an entire HTML file
 allowing the Web designer to modify the appearance of
any tag in the document
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Creating an embedded style
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embedded style, a style applied to various sections
within a Web page
use <style> tag within the <head> … </head> section
within <style> tag, enclose style declarations
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syntax
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<head>
<style type=“text/css”>
style declarations
</style>
</head>
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Embedded Style
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syntax for style declaration:
selector{attribute1:value1; attribute2:value2; ...}
o collection of attributes and values
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selector
o identifies an element in your document, e.g., a heading
o identifies attributes and values within the braces for that
element
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example
<style type="text/css">
h1 {text-align: center; color: red}
</style>
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Embedded Style (contd.)
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Simple Practice exercise:
Using Embedded styles, convert “course description” and
“reference texts” in main.html to blue
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Grouping selectors
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What if there are many tags or blocks which follows
the same style throughout the page?
apply the same declaration to a group of selectors by
including all of the selector names separated by commas
<style type=“text/css”>
h1, h2, h3, h4, h5, h6 {text-align: center; color: red}
</style>
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Now the next level!
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Just the way we changed the styles uniformly in a
single webpage, how about applying that across
multiple webpages, i.e., your website
We now need an external style sheet
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Style types (contd.)
o Inline styles
 styles are added to each tag within the HTML file
 style only affects that particular tag
o Embedded or global styles
 applied to an entire HTML file
 allowing the Web designer to modify the appearance of
any tag in the document
o Linked or external style sheets
 placed in an external file, linked with Web pages
 allowing Web designer to modify the appearance of tags
in several documents across the website
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Creating an external style sheet
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Crate a new text file
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Save it using the extension “.css”,
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Place your styles here
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Within a style sheet, <style> tag is NOT
needed, only need style declarations
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Creating an external style sheet
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Create a text file containing style declarations
/* Author: author name
*/
h1, h2, h3, h4, h5, h6 {text-align: center; color: red}
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Name the file: mystylesheet.css
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Remember:
o Only external stylesheet creation not sufficient
o Need to link the stylesheet and the html pages where you
need the styles
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Linking to style sheets with <link>
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Example: link to a style sheet named “mystylesheet.css,”
<link rel="stylesheet" href="mystylesheet.css" type="text/css" />
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Placement within <head> … </head> of the webpage where
you need the styles
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Style Conflict
Apply external, embedded and inline all three types
of styling with h1 tag
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External:
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Embedded:
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Text-align: center and color: blue
Inline:
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Text-align: center and color: red
Text-align: center and color: green
What is the result?
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Style precedence
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in case of styles conflict, precedence is
determined in the following order:
1. an inline style overrides any embedded style or
external style sheet
2. an embedded style overrides an external style
sheet
3. an external style sheet overrides the internal
style rules set by the Web browser
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Understanding Cascading Order
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Style Inheritance
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If a style is not specified for an element, it
inherits the style of its parent element.
This is called style inheritance
body {color: green}
p {color: red}
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In the above example, the body element is
the parent element
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Practice exercise
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All the elements in my unordered (bulleted)
list must be red throughout the website
All the elements in my ordered (numbered)
list must be blue throughout the website
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CSS Part 2
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What we will cover today…
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2.
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Managing Font-size
Letter and word spacing
Text appearance and attributes
Hyperlinks appearance and attributes
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Managing font size
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in CSS, use font-size attribute to manage font sizes
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body {font-size: some value}
font sizes can be expressed in 4 ways
1. as a unit of length
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Absolute unit
Relative unit
as a descriptive keywords
with a keyword expressing the size relative to the font
size of parent element
as a percentage of the parent element
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1. Unit of length: Absolute units
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use unit of length, absolute units or relative units
o absolute units define the font size based on one of the
following standard units of measurement:
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mm (millimeter),
cm (centimeter),
in (inch),
pt (point; 1pt=1/72in)
pc (pica; 1pc=12pt)
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1. Unit of length: Relative units
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relative unit expresses the font size relative to a size
of a standard character
o em unit is equal to the width of capital letter “M” in browser’s
default font size
o ex unit is equal to the height of a small “x” in default font size
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1. Unit of length: Pixels
a pixel is the smallest element recognized by
the monitor
 text that is 10 pixels high may be perfectly
readable at a low-resolution (e.g., 640 x 480)
monitor, but it can become unreadable at
high-resolution (e.g., 1024 x 768) monitor
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2. Descriptive keywords
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seven descriptive keywords for font size
o xx-small
o x-small
o small
o medium
o large
o x-large
o xx-large
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Example
body {font-size: medium}
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3. Keywords: smaller, larger
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Size relative to parent element
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using keywords “larger” and “smaller,”
o makes the font one size larger or smaller than
the size of parent element
o example: to make <p> paragraph text one size
larger than the body text:
body {font-size: medium}
p {font-size: larger}
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4. Font size as percentage of parent tag
The font size of bold content (defined by <b> tag) is 150% of the size
of surronding text (where the font size is defined by <body> tag)
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Text Appearance and Styling
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Specifying letter, word spacing
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set the space between individual letters
i n d i v i d u a l l e t t e r s
letter-spacing attribute
letter-spacing: size
change the spacing between individual words
individual
words
word-spacing attribute
word-spacing: size
size can be
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any number expressed in the same measuring units used to describe font
size (inches, millimeters, centimeters, em units, etc.)
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Special text attributes
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CSS provides three attributes for special
text effects:
1. text-decoration
2. text-transform
3. font-variant
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text-decoration attribute
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attribute name: text-decoration
values
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none (basically default; no change)
underline
overline
line-through
examples
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text-transform attribute
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attribute name: text-transform
attribute value:
o capitalize
capitalize the first letter of each word in a paragraph
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text-transform attribute
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attribute name: text-transform
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attribute value:
o uppercase
display the text in all capital letters
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text-transform attribute
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attribute name: text-transform
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attribute value:
o lowercase
display the text in all lowercase letters
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text-transform attribute, example
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font-variant attribute
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font-variant attribute create small caps
small caps are capital letters that are the same size
as lowercase letters
syntax
font-variant: small-caps
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font-variant attribute, example
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Contextual Selector
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Working with style inheritance
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Web pages invariably have elements (e.g., tags)
placed within other elements
sample tree structure of Web elements
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Parent and descendant elements
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an element that lies within another element is called
a descendant or descendant element
o e.g., in previous slide, <b> tag is a descendant of <p> tag
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an element that contains another element is called
the parent or parent element.
o e.g., <body> tag is the parent of all other tags used to
format the Web contents
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using the principle of inheritance, styles defined for
a parent tag are transferred to its descendants
tags
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Contextual selectors
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use tree structure to better control styles
o apply a style only to direct descendant of a parent
element, use syntax: e1 e2
o e1 and e2 are the names of HTML elements (i.e.
tags) and e2 is directly below e1 in the tree
structure of elements
o example: li b {color:blue}
only changes the color of the boldface text residing
within a <li> tag to blue
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not all browsers support contextual selectors
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Hyperlink appearance and attributes
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Hyperlink styling
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What is the tag for hyperlinks?
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Introduce the tag for hyperlink as a selector in CSS
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All the attributes discussed so far would work when
applied in CSS
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Hyperlink appearance change
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By default, hyperlinks are blue and have underline
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Change them to red hyperlinks and no underline (default for
my website)
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Change them to red hyperlinks, small caps with lines both
above and below the links
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Hyperlink Special Selector
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a is the general selector
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Link: used for un-visited link
o a:link
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Visited: used for visited link.
o a:visited
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Active: used for the link when it is clicked.
o a:active
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Hover: used for the link when the mouse
hovers over it
o a:hover
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Practice exercise
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Write a CSS file with all the Styles as defined below for the
hyperlinks:
The hyperlinks must be color green with underline textdecoration.
While hovering over the hyperlink with mouse, the hyperlinks
must turn UPPERCASE TEXT, color blue and without any
underline.
The visited hyperlinks must turn into strike through line.
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