Transcript Document

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New Perspectives on Creating Web Pages
with HTML
Tutorial 7: Working with Cascading Style
Sheets
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Tutorial Objectives
• Learn about the history and theory of cascading
style sheets
• Create inline styles, embedded styles, and style
sheets
• Understand style precedence and style inheritance
• Use cascading style sheets to format paragraphs,
lists, and headings
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Tutorial Objectives Continued
• Design a style for hyertext links in their four
conditions
• Define document content with the class and id
attributes and create styles for them
• Mark document content with the <div> and
<span> tags and create styles for them
• Use cascading styles to design page layout
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HTML and Page Layout
• Early versions of HTML had little support for Web
page design.
• The philosophy was to:
– use basic text files that could be quickly downloaded
– rely on Web browsers to format the document’s
appearance
• The simplicity of HTML tags made creating Web
pages easier and made pages load faster.
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HTML and Page Layout
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• Web authors looked for ways to deliver more
visually interesting documents. This has been
done chiefly in three ways:
– using HTML tag extensions
– converting text to images
– controlling page layout with tables
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HTML and Page Layout Upside
• HTML tag extensions: Provide the Web author
with more choices in layout and design.
• Converting text to images: Don’t have to worry
whether a browser will support a particular font.
Place in specific locations on the Web page.
• Tables: Use as a layout tool.
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HTML and Page Layout Downside
• HTML tag extensions: Not all browsers support the
various tag extensions.
• Converting text to images: You are limited in the number
of inline images you can use and still have the page
downloaded in a timely fashion. Moreover, it’s difficult to
make quick changes to the page’s content if you have to
edit the inline graphics first.
• Tables: This makes the HTML files more complicated to
write and to interpret.
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History and Support of CSS
• One principle of design theory is to separate the
content of a document from its design.
• A style defines the appearance of a document element.
• The collection of styles for a Web page or Website is
known as a style sheet.
• Style sheets use a common language and syntax.
• The main style sheet standard is Cascading Style
Sheets (CSS).
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Cascading Style Sheets (CSS)
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• Like HTML, style sheets must use a common language and
follow common rules. This language is known as Cascading
Style Sheets, or more simply, CSS.
• CSS has been developed by the WWW Consortium
(www.w3c.org), the same organization that develops standards
for HTML.
• CSS is designed to augment HTML, not replace it.
• CSS is a whole new way of formatting Web pages.
• CSS provides several tools not available with standard HTML.
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CSS Versions
• CSS1 was released in 1996.
• CSS2 was released in 1998.
• CSS3, the latest standard is being developed.
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Browser Support for CSS
• Browser support for CSS has proven to be uneven.
• Internet Explorer
– Internet Explorer 4.0 provides support for CSS1 standard.
– Internet Explorer 5.0 provides the best support for CSS1, there
are still buys in the implementation of Internet Explorer.
• Netscape
– Netscape’s support for CSS1 has been spotty.
– Netscape has been pushing their own style sheet language over
CSS.
– Netscape is not considered CSS1-compliant, However, Netscape
5.0 may end up supporting CSS1.
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Benefits of Style Sheets
•
•
•
•
•
Use as a design tool.
Makes website more flexible.
Easier to maintain and modify.
More aesthetically interesting.
Consistent look.
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Web Sites with Information on
Cascading Style Sheets
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This figure displays websites that provide more information about the compliance of
browsers with CSS1 and CSS2, and for information about the standards themselves.
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Style Types
• There are three ways of employing CSS in Web pages:
– inline styles in which styles are added to each tag within the
HTML file. The style affects that particular tag but does not affect
other tags in the document.
– embedded or global styles applied to an entire HTML file,
allowing the Web designer to modify the appearance of any tag in
the document.
– linked or external style sheets placed in an external file and
linked with pages in the Web site, allowing the Web designer to
modify the appearance of tags in several documents
• Which approach you choose depends on the Web site’s
design..
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Using Inline Styles
• If you need to format a single section in a Web page, you’d
probably use an inline style.
• To create in inline style, add the style attribute to the
HTML tag using the following syntax:
<tag style=“style declarations”>
– tag is the name of the tag (h1, h2, etc)
– style declarations are the styles you’ll define for a particular
tag
– style declaration must be enclosed within double quotation
marks
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A Style Declaration
• A style declaration consists of attribute names that specify
such features as:
– font size
– color
– font type
• Attributes are followed by a colon and then the value of the
attribute.
• Multiple attributes can be used as long as you separate each
one by a semicolon.
• The general syntax for the style declaration is:
attribute1:value1; attribute2:value2;
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Inserting an Inline Style
This figure shows how to insert an inline style.
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Heading with New Style
This figure shows the heading with the new style.
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Creating an Embedded Style
• An embedded style is a style applied to various sections within a
Web page.
• Insert a <style> tag within the head section of the HTML file.
• Within the <style> tag, enclose the style declarations needed
for the entire Web page.
• The syntax of an embedded style is:
<style type=“style sheet language”>
style declarations
</style>
– style sheet language identifies the type of style language used in the
document
– The default, is “text/css” for use with CSS
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Selectors and Declarations
• Style declaration within the <style> tags obey the following
syntax:
selector {attribute1:value1; attribute2;value2; ...}
– selector identifies an element in your document, such as a heading
or paragraph, and the attributes and values within the curly braces
indicate the styles applied to all the occurrences of that element
– this collection of attributes and values is also referred to as the
declaration of the selector
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Selectors and Declarations Continued
• For example, to display all h1 headings in the HTML
document using a gold sans-serif font, use the following
embedded style:
<style>
h1 {color: gold; font-family: sansserif}
</style>
– h1 is the selector and the text enclosed in the braces is the
declaration
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Defining a Global Style
The type attribute was not included within the <style> tag. This is because
“text/css” is the default style language , and unless you specify a different style
language, you don’t need to enter the type attribute. When using the <style> tags,
you don’t need to include double quotes around the attributes and attribute values.
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Grouping Selectors
• You can apply the same declaration to a group of
selectors by including all of the selector names
separated by commas.
• The following is a sample style declaration to format
all headings in a gold sans-serif font:
<style>
h1, h2, h3, h4, h5, h6 {color:gold; fontfamily:sans-serif}
</style>
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The Same Style Applied
to Two Headings
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Even though the same style is used for all heading tags, there are still some differences
in how the browser displayed text formatted with these tags. Most notably, the styles
did not affect the relative sizes of the text. Text formatted with the <h1> tag is still
larger than text formatted in the <h2> tag. This is because the size of the heading text
was not defined, so that attribute is left to the browser.
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Using an External Style Sheet
• Create styles that apply to an entire Web site by
creating a text file containing style declarations.
• Most style sheets have the extension “.css”,
though this is not a requirement.
• Within a style sheet, you don’t need <style>
tags, just the style declarations.
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Linking to Style Sheets
with the <link> Tag
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• Use the <link> tag to link Web pages to a style sheet.
• The general syntax for using the <link> tag is as follows:
<link href=“URL” rel=“relation_type”
type=“link_type”>
– URL is the URL of the linked document
– relation_type establishes the relationship between the linked document
and the Web page
– link_type indicates the language used in the linked document
• In order to link to a style sheet, the value of the rel attribute should be
“stylesheet” and the value of the type attribute should be “text/css”.
• To link to a style sheet named “mws.css,” the <link> tag would be:
<link href=“mws.css” rel=“stylesheet” type=“text/css”>
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Linking to Style Sheets
with @import
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• Another way to link to a style sheet is to use the @import
command, which accesses the style sheet definitions from
another file.
• To use @import with styles, enclose the @import command
within the embedded <style> tags as follows:
<style>
@import url(stylesheet.css);
style declarations
</style>
– stylesheet.css is the URL of the style sheet file
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The @import Command
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• The @import command provides greater
flexibility than the <link> tag when working
with multiple style sheets.
• The @import command has limited browser
support.
• Unless you have a compelling reason to use
@import, you are probably better off using the
<link> tag.
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Resolving Style Precedence
• In cases where the styles conflict, precedence is
determined in the following order:
– an inline style overrides any embedded style or
external style sheet
– an embedded style overrides an external style sheet
– an external style sheet overrides the internal style
rules set by the Web browser
– any style attributes left undefined by an inline style, an
embedded style, or an external style sheet are left to
the Web browser
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Changing Styles
• As a change is made to a style at one level, the changes are
cascaded through to the other levels (hence the term,
cascading style sheets).
• Where a different font has not been specified, changes will
cascaded through the embedded and inline styles.
• As you define more styles for a Web site, you need to keep
track of the inline, embedded, and external style sheets to
correctly predict the impact that style changes have on the
appearance of each page.
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Working with Style Inheritance
• Web pages invariably have elements placed within
other elements.
– for example, a Web page might have a bold tag, <b>,
placed within a paragraph tag, <p>, to create boldface
text within the paragraph. The paragraph tag is
likewise placed within the <body> tag.
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Sample Tree Structure
of HTML Elements
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This figure displays the HTML element relationship using a tree diagram.
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Parent and Descendant Elements
• An element that lies within another element is called a
descendant or descendant element.
• An element that contains another element is called the
parent or parent element.
• An example of a parent is the <body> tag, which contains
all of the other tags used to format the content of a Web
page.
• Using the principle of inheritance, styles defined for each
parent tag are transferred to its descendants.
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Contextual Selectors
• Use the tree structure concept to better control how
styles are applied to a Web page.
• CSS provides ways of fine-tuning the context in
which the selector is applied.
– if you want to apply a style only to the direct descendant of
a parent element, use the syntax: e1 > e2
– el and e2 are the names of HTML elements and e2 is
directly below the e1 in the hierarchy of elements in the
document
– for example: li > b {color:blue}
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Contextual Selectors Continued
• Not all browsers support contextual selectors
• Always test Web page using various browsers and
browser versions.
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Using Font Families
• The font-family attribute allows you to choose a font face
for use in Web pages.
• CSS works with two types of font faces:
– a specific font, which is a font such as Arial, Garamond, or
Times New Roman that is actually installed on a user’s
computer.
– a generic font, which is a general description of a font,
allowing the operating system to determine which installed
font best matches it.
• CSS supports five generic font types: serif, sans-serif,
monospace, cursive, and fantasy.
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Generic Fonts
This figure shows examples of each generic type.
For each generic font there can be a wide range of designs.
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Generic and Specific Fonts
• One issue with generic fonts is that you cannot be sure which
specific font the Web browser uses to display your text.
• Whenever possible, it is a good idea to use specific fonts.
• Provide the Web browser with several fonts to choose from.
• Browsers that don’t have access to the font you specified as
your first choice may have your second or third choice
available.
• List specific font names first, followed by a generic font name
for the browser to use if none of the specific fonts can be found.
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Managing Font Size
• The <address> tag can format address information
on a Web page.
– by default, text formatted with the <address> tag is
displayed in normal-sized type, italicized, and aligned with
the left edge of the Web page.
• A common method for specifying font sizes with
HTML is to use the size attribute of the <font> tag.
• The size attribute limits you to only seven font sizes.
• Browsers can display font sizes quite differently.
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Managing Font Size Continued
• In CSS, you use the font-size attribute to
manage font sizes. Font sizes can be expressed:
– as a unit of length
– with a keyword description
– as a percentage of the parent element
– with a keyword expressing the size relative to
the font size of the parent element
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Absolute and Relative Units
• If you choose to express size as a unit of length, you can use
absolute units or relative units.
– absolute units define the font size based on one of the following
standard units of measurement: mm (millimeter), cm (centimeter),
in (inch), pt (point), and pc (pica).
– use a relative unit, which expresses the font size relative to a size
of a standard character. There are two standard typesetting
characters, referred to as “em” and “ex.”
– the em unit is equal to the width of the capital letter “M” in the
browser’s default font size
– the ex unit is equal to the height of a small “x” in the default font
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The EM and EX Units
The em unit is more useful for page design, because 1 em is equal to the browser’s
default font size for body text. This is true no matter what font is being used (unlike
the ex unit, whose size changes based on the font face being used).
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The EM and EX Units
• As with absolute units, you can specify factional
values for the em and ex units.
• Unlike the absolute units, em and ex units are
scalable in that they retain their relative
proportions regardless of the monitor size or
resolution.
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Pixels
• Pixels give you the greatest control over size.
• A pixel is the smallest element recognized by the
monitor.
• Pixels should be used with some caution.
• Text that is 10 pixels high may be perfectly
readable at a monitor resolution of 640 x 480, but
it can become unreadable if the monitor is set to
1024 x 768.
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Descriptive Keywords
• If you are uncomfortable dealing with units of length, you
can use one of the seven descriptive keywords:
–
–
–
–
–
–
–
xx-small
x-small
small
medium
large
x-large
xx-large
• These keywords correspond to the seven values of the size
attribute in the <font> tag.
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Expressing Font Size
as a Percentage of the Parent Tag
This figure shows the impact of such a style definition on boldface text in a Web page.
The style has the same impact within a heading, since the heading is the parent
element, and the boldface text is increased to 150% of the surrounding heading text.
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Express a Font Size
using Keywords
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• Express a font size using the keywords “larger”
and “smaller,” which makes the font one size
larger or smaller than the size of the parent
element.
– for example, to make the h2 heading one size larger
than the body text, you could use the following style:
body {font-size: medium}
h2 {font-size: larger}
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Specifying Word, Letter,
and Line Spacing
• Use CSS font attributes to control the spacing
between letters, words, and lines of text.
• To set the space between individual letters, you
use the letter-spacing attribute, with the syntax:
letter-spacing: size
– size can either have the value “normal”, which allows
the browser to determine the letter spacing based on the
font being used, or a number expressed in the same
measuring units used to describe font size (inches,
millimeters, centimeters, em units, etc.)
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Specifying Word, Letter,
and Line Spacing Continued
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• Another technique to change the spacing between individual
words is the word-spacing attribute, with the syntax:
word-spacing: size
– size is either equal to “normal,” to allow the browser to set the
word spacing, or to a specific length using the standard units of
measure
• Use the line-height attribute to modify the vertical space
between lines of text.
• Graphic designers may know this spacing as leading.
• The line-height attribute specifies the minimum distance
between the baselines of adjacent lines.
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Comparison of Line Height
to Font Size
This figure shows how the line height relates to the font size. The line height is
usually larger than the font size to leave additional space between lines of text.
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Line Height
• To set the line height, use the style:
line-height: size
– size is either a specific length, a percentage of the font
size, or a number representing the ratio of the line
height to the font size
– the standard ratio is 1.2, which means that the line
height is 1.2 times the font size
– to make paragraphs double-spaced use the style
definition p {line-height: 2}
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A Title with a Large Font Size
and Small Line Height
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A common typographic technique is to create titles with large fonts and
small line heights. This figure shows an example where the line height is actually
smaller than the font size. This treatment can give the title greater impact than it
would have with more space between the two lines.
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Setting Font Styles and Weights
• Font styles are controlled by the font-style attribute.
• The font-style attribute has three possible values:
normal, italic, or oblique.
• The italic and oblique styles are similar in appearance
though there can be small differences depending on
the font.
• Versions of Netscape prior to 6.0 do not support the
oblique attribute value.
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Font Weights
• CSS considers “bold” to be an aspect of the font’s weight,
or line thickness.
• Font weights can be expressed as an absolute number
ranging in intervals of 100, going from 100 (the lightest)
up to 900 (the heaviest or “most bold”).
• For most fonts, you can assume that:
– a weight of 400 corresponds to normal text
– a weight of 700 can be used for bold text
– a weight of 900 for “extra” bold text
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Font Weights Continued
• Use the keywords “normal” and “bold” in place of a weight
value.
• Express the font weight relative to the parent tag by using the
keywords “bolder” or “lighter.”
• Use the CSS bolder attribute to get bolder text:
h2 {font-weight: 700}
b {font-weight: bolder}
• If these style definitions are applied to a Web page, h2 text
formatted with the <b> tag will be bolder or thicker in
appearance than the surrounding heading text.
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Aligning Text Horizontally
and Vertically
• Use the text-align attribute to left, center, right or
justify text.
• To do this with CSS, use the text-align attribute:
text-align: alignment
– alignment can be left, center, right, or justify
– setting the text-align value to “justify” stretches the
text, extending it from the left to the right margin
– some browsers will ignore the text-align attribute value
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Applying the Center Text-Align Style
This figure shows how to apply the center text-align style.
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Vertically Align Elements
• CSS allows you to vertically align elements such
as text and images relative to the surrounding text.
• The syntax for setting the vertical alignment is:
vertical-align: alignment
– alignment has one of the keyword values
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Values of the Vertical
Alignment Attribute
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This figure shows the alignment keyword values.
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Examples of the
Vertical Alignment Values
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This figure shows an example of each vertical-align value.
Baseline is the default value for vertical alignment.
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Indenting Text
• CSS allows you to indent the first line of a
paragraph.
• The syntax for creating an indentation is:
text-indent: indentation
– indentation is either the length, in either absolute or
relative units, of the indentation or a percentage of the
width of the paragraph
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Hanging Indent
• The length and percentage values also can be
negative, which extends the first line to the left by
the specified value or percentage, and then indents
the rest of the lines in the paragraph.
• This particular effect, called a hanging indent,
works sporadically on many browsers.
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Special Text Attributes
• CSS provides three attributes for special text
effects:
– text-decoration
– text-transform
– font-variant
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Values of the
Text-Decorating Attribute
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This figure shows the text-decoration attribute can be used to underline your text
or place a line over or through your text. You can also make your text blink
on and off using the text-decoration: blink attribute.
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The Text-Transform Attribute
• The text-transform attribute can be used to:
– capitalize the first letter of each word in a
paragraph
– display the text in all capital letters
– display the text in all lowercase letters
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Values of the
Text-Transform Attribute
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This figure shows the effect of the various text-transform values.
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The Font-Variant Command
• Use the font-variant command to create small
caps.
• Small caps are capital letters that are the same size
as lowercase letters.
• The syntax for the font-variant attribute is:
font-variant: small-caps
• Netscape does not support the font-variant
attribute in versions prior to 6.0.
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Values of the Font-Variant Attribute
This figure shows values of the font-variant attribute.
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The font Attribute
• The font attribute provides an efficient way for you to define
multiple attributes.
• The syntax for the font attribute is:
font: font-style; font-variant; font-weight;
font-size/line-height; font-family
– font-style, font-variant, and so forth are the values for font and text
style attributes
• The font attribute requires that you specify the font size, font
variant, and font weight.
• If a font attribute is not included, the browser assigns the
normal or standard value for the element.
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The color Attribute
• CSS works with most of the color names supported by HTML.
• Another way to specify color in CSS is to use RGB color
values.
• You can enter the hexadecimal form of the color value or the
RGB color values directly.
– for example, to change the body text color to teal, use any of
the following styles:
body {color:teal}
body {color: #008080}
body {color: rgb (0,128,128)}
body {color: rgb (0%, 50%, 50%}
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Changing the Color of
the H1-H6 Headings
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RGB color values range from 0 to 255, so specifying a color percentage of 50% for
green and blue is close to a color value of 128. This figure shows an example of
changing the color of the H1-H6 headings.
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Working with Background Color
• By default, elements take on the background color
of their parent element.
• To change the background color of almost any
element, use the background-color style.
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Applying a Background Color
This figure shows how to apply a background color.
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Working with Background Images
• Almost any element on the page can also be displayed with its
own background image.
• The background image has four attributes:
–
–
–
–
the source of the image file
how the image is repeated in the background
where the image is placed on the background
whether the image scrolls with the display window
• To specify which file to use for a background, use the syntax:
background-image: url(URL)
– URL is the location of the image file
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Applying a Background Image
to an Element
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This figure demonstrates how you can apply this style to the <b> tag to create an
interesting design for a section of boldface text.
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Working with Background
Images Continued
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• By default, background images are tiled both
horizontally and vertically behind the element
until the entire element is filled.
• Control the way the tiling occurs using the
background-repeat style attribute.
• The background-repeat attribute has four
possible values.
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Values of the
Background-Repeat Attribute
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This figure shows the background-repeat attributes four possible values.
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Examples of the
Background-Repeat Values
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This figure shows examples of each background-repeat values.
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The Background-Position Attribute
• Background images are placed in the upper-left corner of
their element, and then repeated (if tiling is being used)
from there.
• You can move the background image to a different location
using the background-position style attribute.
• The background-position attribute has two values:
– the first indicates the distance from the left edge of the element
– the second indicates the distance from the element’s top edge
• These values can be expressed as a percentage of the
display area, in units of length, or with keywords.
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Background-Position Keywords XP
and Percentages
This figure shows how background-position keywords relate to the percentage values.
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The Background-Attachment
Attribute
• By default, background images move along with the background
of the page as the user scrolls through the Web page.
• To change the movement of background images, use the
background-attachment attribute.
• The syntax of this style is:
background-attachment: attach
– attached is either “scroll,” to scroll the image along with the
element, or “fixed,” which places the image in a fixed place in the
browser’s display window, preventing it from moving even if the
user scrolls down through the Web page
• The background-attachment attribute is not supported by
Netscape prior to version 6.0.
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Background Images
• Fixed background images are often used to create the impression
of a watermark.
– a watermark is a term that refers to a translucent graphic impressed
into the very fabric of the paper and used in specialized stationery
• If you use a background image that employs a transparent color,
you can combine the background-color and background-image
attributes to create a new image.
– for example, the style:
body {background-color: yellow; backgroundimage: url(logo.gif)}-- displays logo.gif on the
background, and anywhere that a transparent color appears in
the logo the background color yellow will shine through
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The Background Attribute
• You can combine all of the various attributes for
backgrounds into one attribute, called the background
attribute.
• The syntax for the background attribute is:
background: background-color background-image
background-repeat
background-attachment background position
– background-color, background-image, etc., are the values for the
various background attributes
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Using the Background Style Attribute
This figure shows an example of the background style attribute.
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Working with List Styles
• CSS provides more control over the appearance and
behavior of ordered, unordered, and definition lists than
does HTML.
• CSS allows you to specify the types of labels attached to
list items and how to position the labels with respect to the
label text.
• The list-style-type attribute allows you to choose the type
of label to display alongside text formatted with the <ul>,
<ol>, or <li> tags.
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Values of the
List-Style-Type Attribute
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This figure shows the possible values of the list-style-type attribute.
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Creating a Nested Outline Style
Use contextual selectors to create an outline style for several levels of nested lists.
This figure shows a set of contextual selectors used to create an outline style
for different outline levels.
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Using a list-style-image Attribute
• You can create a label, not included in the list-style-type
values, with an image file and the list-style-image
attribute.
• The syntax for applying this attribute is:
list-style-image: url(URL)
– URL is the location and the filename of the image file
• The list-style-image attribute is not supported by Netscape
version 4.7 or earlier.
• It’s a good idea to include the list-style-type
attribute along with the list-style-image attribute.
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Defining the List Style Position
• List items are treated by CSS as if they have an
invisible box around them.
• The syntax for specifying the location of the list
item label is:
list-style-position: location
– location is either “inside” or the default value,
“outside.”
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Defining the Position of the List Label
This figure shows that the labels for the list items can be placed either outside or inside the box.
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The list-style Attribute
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• You can combine all of these attributes into the
list-style attribute.
• The syntax for this style is:
list-style: list-style-type list-styleimage list-style-position
– list-style-type, list-style-image, and list-style-position
are the attribute values for each of the individual list
style attributes
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Defining the Appearance
of a List Label
XP
This figure shows how to define the appearance of a list label.
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Formatting Hypertext Links
• Hypertext has an additional attribute that normal text
doesn’t have: the condition of the hypertext link itself.
• A hypertext link can be in one of four states:
–
–
–
–
the link’s target has already been visited by the user
the link’s target has never been visited by the user
the link is currently being clicked by the user
the user’s mouse pointer is hovering over the link
• Web browsers provide a visual clue for each of these
states, such as a different color for visited links, and a
different shape for the pointer when it is hovering over a
link.
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Formatting Hypertext Links
Continued
XP
• CSS provides a different selector for each condition.
• The general syntax is:
a:visited {styles for previously visited targets}
a:link {styles for targets that have never been visited}
a:active {styles for links that are currently being clicked}
a:hover {styles when the mouse cursor is hovering over the
link} - this is called a rollover effect
• You can use a variety of CSS attributes to create a different style for each
condition.
– for example, to change the color of previously visited targets to red, use
the style:
a:visited {color:red}
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Creating a Rollover Effect
This figure shows the rollover effect.
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Working with ids and Classes
• A pseudo-class is a classification of an element based on
its status or its use.
– in the example of the rollover effect, the status was the
condition of the hypertext link
– the element itself, a hypertext link with the pointer located
over it, is called a pseudo-element
• CSS introduces additional pseudo-classes, including the
first-line pseudo-class and the first-letter pseudo-class,
which are used for formatting the first line and first letter
of a block of text, respectively.
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Applying a Style to a Pseudo-Class
This figure shows how to apply a style to a pseudo-class and what it would like in the browser.
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The class Attribute
• Many browsers do not support the first-letter and first-line
pseudo-classes yet.
• The only pseudo-classes widely supported are the four
hypertext link conditions.
• You can create customized classes by adding the class
attribute to HTML tags.
• The syntax for creating a class is:
<tag class=“class_name”>
– tag is the HTML tag
– class_name is the name of the class
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Applying a Style to a Pseudo-Class
This figure demonstrates creating an inline style for the h1 heading with the class name “First
Header.” This technique is useful when you have multiple Web pages in which you want the
first heading in each page to be formatted in the same way.
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The id Attribute
• Closely related to the class attribute is the id attribute, which
applies an id to a specific element in the document.
• The id attribute must be unique; there can not be more than
one tag with the same id value.
• The syntax for creating an id is:
<tag id=“id_name”>
– tag is the HTML tag
– id_name is an id name assigned to the tag
• The class and id attribute are useful HTML features to use
with CSS to define styles for specific content without using
inline styles.
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Creating a Class for Monthly Specials
This figure shows how to create a class for monthly specials.
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Working with Container Elements
• HTML supports two types of container types:
– the <span> tag, which is used to contain inline
elements such as individual letters, words, phrases, or
inline images
– the <div> tag, which is used to group blocks of text
such as paragraphs, block quotes, headings, or lists.
Collectively, these text blocks are known as block-level
elements
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Using the <div> Tag
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This figure shows an example in which a heading and a paragraph have been enclosed
in a <div> container. The <div> tag does not actually format the block-level
elements; it merely groups them as a unit. For this reason, the <div> tag always
includes either a class or id attribute that identifies that group.
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Using the <div> and <span> Tags
This figure shows an example of how the <span> tag can be used to format a selection
of text within a paragraph. A <div> tag is used to format the entire paragraph. You
almost always include an id or class attribute with the <span> tag.
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Formatting Block-Level
Element Boxes
• With CSS, you can control the layout of a Web page by manipulating
the size and location of block-level elements.
• CSS treats all block-level elements as a group.
• HTML tags that can be treated as block-level elements are:
–
–
–
–
–
–
–
–
–
<h1> - <h6> tags
<p> tag
<blockquote> and <address> tags
<ul>, <ol>, and <dl> list tags
<li>, <dt>, or <dd> tags (individual list items)
<div> tag
<body> tag
<hr> tag
<img> tag
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Parts of the Block-Level Element Box
• There are three elements:
– margin between the box and the parent element
– border of the box
– padding, which is the space between the box around
the block-level element and the border
• CSS provides attributes you can use to control the
appearance and behavior of each of these
elements.
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Features of the Box Around
a Block-Level Element
XP
This figure shows features of the box around a block-level element.
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Some Block-Level Elements
in a Web page.
XP
This figure shows some of the boxes in a Web page.
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Controlling Margins
• The margin is the space between the block-level element
and the parent element.
• There are four attributes that control the margin size:
– margin-top - the space between the top of the box and the
top margin
– margin-right - the space between the right side of the box
and the right margin
– margin-bottom - the space between the bottom of the box
and the bottom margin
– margin-left - the space between the left side of the box and
the left margin
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Controlling Margins Continued
• Margin sizes can be expressed in units of length (points,
pixels, em units, etc.) or as a percentage of the width of the
parent element box.
• Use the “auto” value, which allows the browser to
determine the margin size.
• A margin size can be negative, although this can lead to
unpredictable results when viewed with certain browsers.
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Creating an Overlay Effect
Web page designers can use negative margins to place one block-line element on top of another,
creating an “overlay” effect. This figure shows an example of an overlay effect.
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Controlling Margins Continued
• The four margin attributes can be combined into a single attribute
with the syntax:
selector {margin-top margin-right margin-bottom
margin-left}
– if you only include three values in the combined attribute, they are
applied in the following order: top, right, bottom, and the browser
sets the left margin to match the right margin
– if two values are specified, they are applied to the top and right
margins, and the browser sets the bottom and left margins to match
the top and right margins
– if only one value is entered, the browser applies the value to all
four margins
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Setting Padding Size
• Padding refers to the amount of space between
the element and its border.
• Four attributes are used to control the size of the
element’s padding:
–
–
–
–
padding-top
padding-right
padding-bottom
padding-left
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Formatting the Border
• CSS provides a variety of attributes for managing the box’s
border width, border color, and border style.
• To combine all of the border attributes, use the syntax:
border: border-width border-style border-color;
• These attributes can be applied to all four borders at once, or
you can work with individual borders.
• There are a variety of ways with which border styles can be
expressed.
• Support for the border declaration is inconsistent across
browser types and versions.
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Different Border Attributes
The figure
summarizes the
various border
attributes.
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Example of Border-Style Values
Border widths can be
expressed using units
of length or with the
keywords thin,
medium, or think.
The border color can
be defined using color
names or color values.
This figure shows that
each of the nine
different styles that
can be applied to a
border.
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Formatting the Width and
Height of Block-Level Boxes
• To change the width of a box, use the width attribute.
• Box width can be expressed in terms of absolute or
relative units of length, or as a percentage of the width of
the parent element.
– for example, the style:
body {width: 75%}
– reduces the width of the Web page body to 75% of the width of the
browser’s display area
• The width attribute is seldom used except with text boxes
and inline images.
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Formatting the Width and Height of
Block-Level Boxes Continued
• The height attribute sets the height of the element.
• Heights can be expressed in absolute or relative lengths,
but not percentages.
• Typically, you won’t set the height of a block-level element
because problems can arise when the amount of text in the
element exceeds the height allowed.
• The height attribute is usually applied to inline images
and little else.
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The float Attribute
• The float attribute works like the align=“left”
or align=“right” attributes used with the <img>
tags.
• This attribute places the block-level element on
the left or right margin of the parent element.
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Floating a Block-Level Element
This figure shows that
when a browser
encounters the float
attribute, it moves the
element over to
whatever margin the
Web author has
specified and then
brings the next blocklevel element up. The
text in that element is
wrapped around the
floating element.
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Using the clear Attribute
XP
Prevent other elements
from wrapping around
the floating element by
adding the clear
attribute to the element
below the floating
element.
When the value of the
clear attribute is set to
“right,” the browser
displays the element on
the page at the point
where the right margin
is clear.
Other possible values
for the clear attribute
are “left” and “both”
(for both margins).
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An Example Web site
This figure shows an example Web site with the features discussed in this tutorial.
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Tutorial 7 Summary
• Learned about the history and theory of style sheets.
• Covered the three types of style sheets: inline, embedded
or global, and linked or external style sheets.
• Covered the syntax of style, describing selectors,
attributes, and attribute values.
• Learned how to group selectors to apply the same style to
multiple tags.
• Learned how a browser resolves style precedence and style
inheritance.
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Tutorial 7 Summary Continued
• Discussed parent and descendant elements and contextual
selectors.
• Focused on applying different style attributes to Web page
elements.
• Examined font and text attributes including word and letter
spacing, font styles and weights, and text alignment.
• Learned how to apply color and background attributes.
• Covered the style attributes that can be applied to lists.
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Tutorial 7 Summary Continued
• Learned how to apply styles to hypertext.
• Learned about pseudo-elements and pseudo-classes in
order to create rollover effects (Internet Explorer only).
• Discussed general classes and id’s.
• Covered style attributes of all block-level elements..
• Learned how to control the margin, padding, and border
attributes of their block-level elements.
• Covered the float attribute to control the placement of a
<div> tag on the Web page.
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