css-presentation.ppt

What are Cascading Style Sheets?
 Cascading Style Sheets (CSS) allows for more control over the look, or
style, of web pages or other XML files by providing a central location,
or sheet, where you can define how certain HTML (Hyper-Text Markup
Language) or XML (eXtensible Markup Language) tags are going to be
interpreted by the browser.
 Why is it called “cascading”? In CSS, multiple styles can be applied to
a particular document (usually a web page or XML file). The browser
will interpret these styles in a cascading fashion:
• Style rules set up site-wide are overridden by styles located within individual pages.
• Individual pages are overridden by styles inside an individual tag.
• In addition, the end user can set up styles in the browser that will override the author’s
styles.
• All matching rules for a particular selector will be applied, except where they conflict
with each other (in which case, the latter rule would be applied, as determined by the
cascade). In the following example, <h2> tags would be displayed in red and italics
(but not blue):
h2 {font-style: italic;}
h2 {color: darkblue;}
h2 {color: red;}

Pros and Cons of Using CSS
 Pros
• Greater designer control of the appearance of the page
• Easier management of site-wide changes
• Greater accessibility to web sites by non-graphical browsers and
web-page-reading software
 Cons
• Different browsers may interpret Style Sheets in different ways
• Some styles may not be seen at all on some browsers

CSS Basics
 Under standard HTML, to create a web site with
<h2> tags that have the standard features of a Header
tag (that is, their own paragraph, bold, with a size
change) and also are dark blue, you have to code each
one as follows:
<h2><font color="darkblue">This is a darkblue H2 tag</font></h2>
 That’s a lot of information to type every time you
want to use a dark blue <h2> tag. Using CSS, all you
need to do is type a regular <h2> tag. The style
information will be included in the Style Sheet as
follows:
h2 { color: darkblue;}

CSS Rules
 To change the color of ALL <h2> tags from darkblue to green,
simply change the called for color to “green.” The next time
anyone sees the site, all the <h2> tags on all the pages will be
green instead of darkblue.
 These styles are called rules. Each rule consists of a selector and
a declaration (which is made up of a property and a value).
 In the example below, h2 is the selector, color is the property,
and darkblue is the value. When used with web pages, selectors
are usually HTML tags.
h2 { color: darkblue;}
 Syntax for a CSS rule:
selector { property: value; }

Grouping Styles and Selectors
 Each rule can include multiple styles by simply separating them by semicolons:
h2 { color: darkblue; font-style: italic;}
 Additionally, multiple selectors that have the same styles can be grouped by separating them with commas:
h1, h2, h3 { color: darkblue; font-style: italic;}
 Contextual selectors allow you to specify that something will change, but only when it is used in conjunction
with something else. With the following style, strong will be displayed in red, but only when it occurs
within li within ul.
ul li strong { color: red;}
Elements being modified by contextual selectors need not appear immediately inside one another (using
this style, blah would still be red text: <ul><ol><li><strong> blah </strong></li></ol></ul>).
 Direct child selectors allow you to specify that something will change, but only those that are immediately
inside of another element. With the following style, only those strong elements that are directly inside of
an h1 will be purple; no strong tags deeper within the sheet will be purple.
h1 > strong { color: purple;}
 Adjacent selectors allow you to specify that something will change, but only when preceded by something
else. With the following style, only those links (a) that are preceded by an h2 will be green.
h2 + a { color: green;}
Elements being modified by adjacent selectors appear immediately after one another. Using this style, this
link would be green: <h2>Visit Stanford!</h2><a href="http://www.stanford.edu">click here</a>.
This link would not: <h2>Visit Stanford! <a href="http://www.stanford.edu">click here</a></h2>.

Where do you put the styles?
 Style information can be located in three places:
• External to the pages in a site
• Internal to each page
• Inline with individual tags
 Generally, creating an external style sheet file is the
preferred method. To take full advantage of CSS, the
Style Sheet for a site should be in this one external
file, so that any changes will apply throughout the
site. This also means that only one style document
has to be downloaded for a single site.

External example
Text that appears in the basic.css style sheet document:
h2 {font-family: Arial, sans-serif; font-style: italic; color: green;}
p {font-family: Courier, monotype; font-style: bold; color: red; }
Text that appears in the print.css style sheet document:
h2 {font-family: Book Antiqua, Times, serif; font-style: italic; }
p {font-family: Courier, monotype; font-style: bold; }
HTML document, using the <link> tag method
<head>
<link rel="stylesheet" type="text/css"
href="basic.css" media="all" />
<link rel="stylesheet" type="text/css"
href="print.css" media="print" />
</head>
HTML document, using the @import and @media method
<head>
<style type="text/css">

</style>
</head>

Style Location: Internal
 Style information can also be included in the <head>
section of an individual web page. This tends to work
best when a single page needs to have a slightly
different look than the rest of the site.

Style Location: Inline
 For extreme control, style information can be
included in an individual tag. The style effects only
that tag and no others in the document. This option
is most useful for those rare occasions when a single
tag needs to have a slightly different style.

Hierarchy of styles
 When style information is located in all three places in one site,
the hierarchy is as follows:
• External Style Sheets affect the entire site.
• Internal styles affect only their own pages and override external styles.
• Inline styles affect only their own tags and override both internal and
external styles.
 For example, if an external Style Sheet sets <h2> tags to purple
and a particular page has an internal style that changes that
color to orange, the <h2> tags will be orange only on that page
and nowhere else in the site. If there is a single <h2> tag on that
page which specifies green as its color, then the color for that
one tag will be green. All other <h2> tags on that page would
be orange; the <h2> tags on the rest of the site would be purple.

!important
 Normally, the last rule listed in the cascade will take precedence
over previous rules. In this example, the body font will be
Verdana, not Times.
body {font-family: Times;
font-family: Verdana;}
 However, by entering !important in a rule, that rule will take
precedence, regardless of its location. In this example, the body
font will be Times, not Verdana.
body {font-family: Times !important;
font-family: Verdana;}
Note: !important does not work with all properties in Internet Explorer.

Classes and IDs
 HTML has two attributes that make CSS even more useful: class and ID. They
make it easy to apply style to just about any tag.
 Classes can describe a generic style that can be applied to any HTML element, or
can be created for specific elements.
 When defining a style for elements with a particular class attribute in the Style
Sheet, declare a rule using a dot (.) followed by the class name. To limit the style
to a particular element with that class attribute, use a selector combining the tag
name with a dot followed immediately by the class name.
• The following rule would apply to any element with the attribute class=“shade"
.shade { background: yellow; }
• The following rule would apply only to paragraph tags with the class shade (<p class="shade">)
p.shade { background: red; }
 IDs are similar to classes, but IDs are unique – they can only be used with one
instance of an element within a document.
 When defining a CSS rule using an ID-based selector, use a
number/pound/hash sign (#) followed by the style name. To limit the style to a
particular element with that id attribute, use a selector combining the tag name
with a # and then the id name.
• The following rule would apply to any element with the attribute id="intro"
#intro { font-size: 2em; }
• The following rule would apply only to heading 1 tags with the id intro (<h1 id="intro">)
h1#intro { color: green; }

Class example
 Here’s an example of a web page with an internal CSS
style with a class called “highlight”:

Inline vs. Block Display (HTML)
 All HTML elements (tags) are assigned a display
property value of either inline or block.
 Inline elements display in browsers horizontally.
[INLINE ELEMENT 1] [INLINE ELEMENT 2] [INLINE ELEMENT 3]
 Block elements display in browsers vertically (stacked
one on top of the other).
[BLOCK ELEMENT 1]
[BLOCK ELEMENT 2]
[BLOCK ELEMENT 3]
 Examples of inline elements:
<a> <img> <strong> <em> <span>
 Examples of block elements:
<p> <h1-h6> <div> <hr> <table> <ul> <ol>

Inline vs. Block Display (CSS)
 Using CSS, you can change this inherent display
property:
• To force a block display, use the declaration display: block;
• To force an inline display, use the declaration display: inline;
• To force a list, use the declaration display: list-item;
• To hide elements matching the selector, use the declaration
display: none;

Example – display: block;
 Normally, <a> tags display inline.
 But, if you add the style a {display: block;},
they will display as a vertical navigation menu:

Example – display: inline;
 Normally, the heading tags display in block format:
 But, to have them display inline, add the style
h1,h2,h3 {display: inline;}:

Span and Div
 There are two tags that are particularly useful when
using CSS: <span> and <div>. They are both
container tags that have minimal formatting
associated with them.
 The <span> tag is an inline element that simply
holds text without doing anything special to it.
 The <div> tag is a block element and causes the text
it encloses to start on a new line.
 Using <span> and <div> tags in conjunction with
classes and IDs allows for great flexibility in creating
pages.

Example using SPAN, DIV, Class, and ID
 Here’s an example of a web page using a class, an id,
and the span and div tags:

Unit Measurements
 In CSS, you can measure units either in absolute values or in relative values.
 Absolute values are fixed, specific values. Since they are exact measurements, they allow
the designer complete control over the display of the web pages.
mm, cm, in, pt, pc, xx-small, x-small, small, medium, large, x-large, xx-large
 Relative values have no fixed, specific values, and are calculated in comparison to
something else (usually the size of the default font or line size). Because different computers
have different video cards, screen sizes, and users have differing eyesight abilities, relative
values tend to be a better choice. They give the designer less absolute control but it often
creates a better experience for the visitor.
em, ex, px, larger, smaller, num%
 Examples:
body { font-size: 12px; }
h1, h2, h3 { line-height: 200%;}
 Note – a warning about using percentages: if you use percentages, and nest an element
inside of that same element, the percentages will be cumulative.

Font and Text Styling
When choosing a font, there are several things to keep in mind:
1. Not everyone has the same set of fonts.
2. If you use a font that the visitor doesn’t have, the page will display in the
default font (usually Times), unless you provide more choices. To do this,
add more than one font in your declaration, and always end with the font
family (serif, sans-serif, or monospace):
font-family: Verdana, Arial, Helvetica, sans-serif
3. Documents designed to be printed tend to look better in Serif fonts (Times,
Georgia, Book Antiqua, etc.)
4. Documents designed to be viewed onscreen tend to look better in Sans-serif
fonts (Verdana, Arial, Helvetica, etc.)
To apply a font to the entire web page, modify the body tag:
body {font-family: Verdana;}
To apply a font to a specific section of text, create a class, and use
the span tag with that class:
.neatstuff {font-family: Comic Sans MS;}
<span class="neatstuff">This is in Comic Sans</span>

Modifying List Elements
 By default, unordered lists (<ul>) appear as bullets and ordered
lists (<ol>) appear as numbers in HTML.
 Using CSS, you can modify how list items will appear:
• Properties:
list-style, list-style-type, list-style-image, list-style-position
• Values:
disc, circle, square, decimal, decimal-leading-zero, lower-roman,
upper-roman, lower-alpha, upper-alpha, lower-greek, lower-latin,
upper-latin, hebrew, armenian, georgian, cjk-ideographic, hiragana,
katakana, hiragana-iroha, katakana-iroha, none, url("graphic.gif")
 Examples:
ul { list-style: disc; }
ol { list-style: upper-roman;}
li { list-style: url("blackball.gif");}
ul li { list-style-position: inside;}

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