Styling the New Web
Web Usability with Style Sheets
A CHI 2002 Tutorial
Steven Pemberton
CWI and W3C
Kruislaan 413
1098 SJ Amsterdam
The Netherlands
Steven.Pemberton@cwi.nl
www.cwi.nl/~steven
Table of Contents
Agenda
About the Instructor
Objectives
Block 1
Block 2
Block 3
Block 4
Resources
Quick reference to CSS1
Very Quick Reference to CSS1
Agenda
The day is split into four blocks, each of 90 minutes.
Each block consists of about 45 minjutes lecture, followed by 45 minutes
practical.
The breaks between blocks are 30 minutes, with 90 minutes for lunch.
Block 1
Introduction, basic CSS: selectors, fonts, colours.
Break
Block 2
Intermediate level: advanced selectors, inheritance, margins, borders,
padding.
Lunch
Block 3
Advanced: text properties, background, positioning, cascading.
Break
Block 4
The Future: XML and XHTML.
About the Instructor
Steven Pemberton is a researcher at the CWI, The Centre for Mathematics
and Computer Science, a nationally-funded research centre in Amsterdam, The
Netherlands, the first non-military Internet site in Europe.
Steven's research is in interaction, and how the underlying software
architecture can support the user. At the end of the 80's he built a
style-sheet based hypertext system called Views.
Steven has been involved with the World Wide Web since the beginning. He
organised two workshops at the first World Wide Web Conference in 1994,
chaired the first W3C Style Sheets workshop, and the first W3C
Internationalisation workshop. He has been a member of the CSS Working Group
from its start, and is a long-time member (now chair) of the HTML Working
Group, and co-chair of the XForms Working Group.
Steven is Editor-in-Chief of ACM/interactions.
Objectives
HTML has been for too long, and incorrectly, seen as a purely presentation
language. It was originally designed as a structure description language, but
extra elements were added later by browser manufacturers in order to
influence the presentation. This has had the effect of limiting Web site
usability by introducing presentation elements that slow down Web access,
reduce or prevent accessibility to the sight-impaired, and reduce the
end-user's options when viewing a document.
The World Wide Web Consortium (W3C) started the Style Sheet activity in
1995 in order to get HTML back to its pure form. The result of this was
Cascading Style Sheets (CSS), which allows the separation of content and
presentation in Web sites. Using style sheets has many benefits,
including:
- Separation of content and presentation means that Web pages are easier
to write.
- Since images are no longer needed to represent styled text, Web pages
download significantly faster.
- By separating out the presentation elements, blind and other
sight-impaired users are able to access the Web much more easily,
especially since CSS explicitely supports aural browsers.
- By allowing style sheets to specify sizes in relation to other sizes,
rather than as absolute sizes, people with reduced sight can scale pages
up and still see them as they were intended.
- You can now design the look of your site in one place, so that if you
change your house style, you only need to change one file to update your
entire site.
Even if the Web remained based on HTML, these would be enough reasons to
use style sheets. However, the Web is now going in a new direction: XML, and
XML has no inherent presentation semantics at all. To use XML you have to use
a style sheet to make your site visible.
As a part of the movement to XML, a new version of HTML, called XHTML, is
being developed. Since all presentation-oriented elements are being dropped,
style sheets will become essential there too.
So the objectives of this course are to give an advanced introduction to
the use of CSS to style HTML and XML documents, and to show how this can
improve usability, and to give an introduction to the use of XML and
XHTML.
CSS level 1 will be presented, since this is the version currently widely
implemented, with pointers to what is in CSS 2, and what can be expected in
CSS 3.
These notes have been produced entirely in XHTML and CSS, using different stylesheets for printing, screen use, and presentation.
Course Plan
- Introduction, basic CSS: selectors, fonts, colours; Practical
- Intermediate-level stuff: advanced selectors, inheritance, margins,
borders, padding; Practical
- Advanced stuff: text properties, background, positioning; Practical
- The Future: XML and XHTML; Practical
HTML and SGML
- HTML (up to now) has been an SGML application.
- SGML is intended to define the structure of documents
For instance, <H1> </H1> defines a heading without
specifying how it should look.
<UL> <LI>... </UL>
specifies a list of items.
- These classifications often have semantic significance. <I> and
<B> were mistakes, use <EM> and <STRONG> instead
Contamination
- Netscape started to add their own tags, based on the idea that with
their market penetration they could get a head start.
- Unfortunately most tags added by Netscape are presentation-oriented
tags – which do not fit in the structure orientation of standard
HTML – such as <BLINK> and <FONT>
- These do specify how the item should look, and have no inherent
semantics; Microsoft also followed suit.
Style Sheets
- In order to get HTML back to being a structure language, W3C hosts work
on Style Sheets, and producing a Style Sheet Language CSS –
Cascading Style Sheets.
- Aims:
- easy to write
- easy to implement
- has a development path.
- CSS is a 90% solution
- For all typesetting possibilities XSL is being developed
CSS
- CSS is a language that allows you to specify how a document, or set of
documents, should look.
- Advantages:
- Separates content from presentation
- Makes HTML a structure language again
- Makes HTML easier to write (and read)
- All HTML styles (and more) are possible
- You can define a house style in one file
- Accessible for the sight-impaired
- You can still see the page on non-CSS browsers
- CSS is also an enabling technology for XML
Separating Content and Presentation: Author Advantages
- Easier to write your documents
- Easier to change your documents
- Easy to change the look of your documents
- Access to professional designs
- Your documents are smaller
- Visible on more devices
- Visible to more people
Separating Content and Presentation: Webmaster Advantages
- Separation of concerns
- Simpler HTML, less training
- Cheaper to produce, easier to manage
- Easy to change house style
- Reach more people
- Search engines find your stuff easier
- Visible on more devices
Separating Content and Presentation: Reader Advantages
- Faster download (one of the top 4 reasons for liking a site)
- Easier to find information
- You can actually read the information if you are sight-impaired
- Information more accessible
- You can use more devices
Separating Content and Presentation: Implementor Advantages
- Improves the implementation (separation of concerns)
- Can produce smaller browsers
Levels
- CSS has been designed with upwards and downwards compatibility in mind.
- CSS1: basic formatting, fonts, colours, layout; quick and easy to
implement
- CSS2: more advanced formatting; aural style sheets
- CSS3: printing, multi-column, ...
- In general a valid CSS1 style sheet is also a valid CSS2 style
sheet.
- In general a CSS2 style sheet can be read and used by a CSS1-supporting
browser.
Check your log files!
- More than 95% of surfers now use a CSS1-compatible browser:
- Microsoft IE 3, 4, 5, 6
- Netscape 4, 6
- Opera 3.5, 4, 5, 6
- While the quality of the support for CSS on these browsers is varied,
you never need to use the <FONT> tag again!
- Today we'll be largely talking about CSS1, since it is widely
implemented
Why is Usability Important for Websites?
Forrester did research among 8000+ users on why they chose one website above another equivalent one. Reasons were:
- Content 75%
- Usability 66%
- Speed 58%
- Freshness 54%
All other reasons were 14% or lower.
CSS can't help you with Content or Freshness, but it can with the other two!
Why is CSS good for usability?
- Presentation is not hard-wired in the HTML
- Users can make their own choices (font size, colours, etc), and
override the documents
- Pages load faster
- Pages become more accessible for the sight-impaired (who can use speech
browsers)
- Pages are viewable on a wider range of platform types
Using CSS
Normally, you put your CSS descriptions in an external file, and link to that from your HTML:
<html>
<head>
<link rel="stylesheet"
type="text/css"
href="your-filename.css">
</head>
<body> ...</body>
</html>
Inline style is also possible
You can also put your style sheets in the head of your HTML document:
<head>
<style type="text/css">
h1 { color: blue }
</style>
</head>
For many reasons, it is better to use external style
sheets
Style sheets for XML
For XML use a processing instruction:
<?xml-stylesheet type="text/css"
href="your-filename.css"?>
Put before first element of the document
HTML Style Attributes
HTML also allows you to use a STYLE attribute:
<P STYLE="color: red">Stop!</P>
This is bad practice, and undoes many of the advantages of
CSS.
Doesn't (necessarily) work for XML.
Comments
- Comments are expressed between /* and */
- Example:
/* This is a comment */
Basic Selectors
- Basic selectors are just element names
- Several rules can be joined together using the comma:
- H1, H2, H3, H4, H5, H6 { font-family: helvetica, sans-serif}
- Don't use html as a selector: use
body instead
Examples
- h1, h2, h3 { font-family: helvetica, sans-serif }
- body { color: white; background-color: black }
- p { text-align: justify }
All matching rules apply
You can have as many rules as you like for a selector. All rules that apply to an element get applied. Clashing declarations are resolved by giving priority to more specific selectors, and later rules.
So
h1 {font-weight: bold}
h1 {font-size: 200%}
is equivalent to
h1 {font-weight: bold; font-size: 200%}
Styling text
There are a number of properties for affecting the style of text:
- font-size, font-weight, font-style, font-family, and
font-variant
- line-height, vertical-align, word-spacing, letter-spacing
- text-align, text-decoration, text-transform, text-indent
font-size
- You can use absolute or relative sizes. Relative sizes are in relation
to the parent element (e.g. <body>)
- Example: h1 {font-size: 200%}
- Example absolute sizes:
10pt, small, medium, large,
x-small, xx-small, x-large, xx-large
- Example relative sizes: larger, smaller, 120%, 1.2em
- Initial value is medium
Using relative sizes makes your site more accessible
Warning about 'initial values'
- Most CSS properties have 'initial values'
- 'Initial value' means 'if no other value has been assigned'
- For HTML (but not XML) most values have been assigned by the browser already
- Example: 'font-size' has an initial value of 'medium', but the browser
will likely have set a larger value for <h1>
Lengths
Relative:
- Ems: 4em
- X height: 1ex
- Percentages: 120%
Absolute:
- Pixels: 12px (A pixel is not a hardware unit)
- Inches: 0.5in
- Cm: 2.5cm
- Mm: 25mm
- Points: 10pt
- Picas: 2pc (1pc = 12pt)
font-weight
- Values: normal, bold, bolder, lighter, 100, 200, ..., 900
- normal = 400
- bold = 700
- Initial is normal
- Example: h1, h2, h3 {font-weight: bold}
font-style
- Values: normal, italic, oblique
- Initial: normal
- If you specify italic, but the font only has an oblique, you
get that (but not vice versa)
- Example: em {font-style: italic}
font-family
- Values: a list of font names, followed by a generic font
- Generic fonts are: serif, sans-serif, monospace, cursive, fantasy:
Serif, sans-serif, monospace, cursive,
fantasy
- Each font in the list is tried in turn until one is found
- Example:
h1, h2, h3 {font-family: arial, helvetica,
sans-serif}
- Initial value depends on browser
You should always end with a generic family
Colours: color and background-color
- The foreground colour (text, borders, etc) is given with the
color property
- The background colour is given with the background-color
property
- Values are 16 colour names: black, white, gray, silver, red, maroon,
yellow, olive, green, lime, blue, navy, purple, aqua, fuchsia, teal,
or #F00, #FF0000, rgb(255, 0, 0), rgb(100%, 0, 0)
- Example: body {color: black; background-color: white}
Practical 1
- Here is a file called practical1.html. View it with the
browser, to see what the defaults look like.
- Create a CSS file called practical1.css, and edit the HTML file to use
it.
- Make the following changes to the presentation:
- <em> elements should have a yellow background
- Headings should be in a sans-serif font
- Look at the results.
- Now make the presentation white text on blue.
- What colours are aqua, fuchsia and teal?
Class Selectors
- If an element has a class attribute, you can select on it
- In the CSS:
p.important { color: red }
- In the HTML:
<p class="important">Do not phone
before 09:00!</p>
- or all "important" elements regardless of type:
.important { color: red }
Use of HTML: span
- Use the <span> element as a carrier of class
information:
Do <span
class="important">not</span> cross
- If you want such text to be styled in some way on non-CSS browsers as
well, use <strong> or <em> instead:
Do <em
class="important">not</em> cross
Do <strong
class="important">not</strong>
cross
ID Selectors
Used rarely; class is more useful
Contextual Selectors
These allow you to address the nesting of the document:
h1 { font-weight: bold }
em { font-style: italic }
<h1><em>Now</em> is the time!</h1>
Now is the time
h1 em { font-weight: normal }
Now is the time
Examples of contextual selectors
- em { font-style: italic }
- em em { font-style: normal }
Nested em's revert to normal font
- ul li { font-size: medium }
- ul ul li { font-size: small }
- ul ul ul li {font-size: x-small }
Nested unordered lists use smaller fonts
- More specific selectors take precedence (more later)
Inheritance
- Note that in
h1 { color: blue }
<h1><em>Now</em> is the time</h1>
Now is the time
that the <em> element is also blue. It is inherited by the
<em> element.
- Many properties are inherited, but some are not:
h1 { border-style: solid }
Now is the time
If the border-style were inherited by the <em>, you would
get:
Now is the time
display
- Some elements (like <em>, <span>) are inline. Others (like
<p>, <h1>) are blocks. The display property
specifies this for the presentation
- Values: block, inline, list-item, none
- Block: says that the element represents a block
- Inline: that the element represents inline text
- list-item: that the element is a list item (<li> in HTML) (more
properties later)
- none: the element is not displayed at all.
- Initial value: not important for HTML; different for CSS1 and CSS2, so
never assume a default!
text-align
- Values: justify, left, right, center
- Applies to blocks (I.e. elements with display: block or list-item)
- Initial: not defined
Box model
- All elements have this box model.
- The margin's colour is transparent
- The border's colour can be set
- The padding has the same colour as the background colour of the
content
Box model: height and width properties
- The 'height' and 'width' properties of an element affect the height
and width of the 'content' box
- So if you set the width to 4em, the padding to 3em, the border to 2em, and the margin to 1em, the width of the whole box will be (4 + 2×3 + 2×2 + 2×1) = 15em. (But see note later on 'auto' values).
Box model: margin, border, padding
Margins: margin-top, -right, -bottom, -left
- Examples of values: 0, auto, 2em, 3pt, 1%, ...
- Initial: 0
- Margins are in relation to enclosing element
- Percentage values refer to width of containing element
- Example: p { margin-left: 3em }
- Negative margins are allowed!
- Margins are transparent, so enclosing element's background shows
through
- auto means 'as calculated by the browser' (see
width).
Warnings about use of margins
body {margin-left: 4em}
h1 {margin-left: -4em}
<h1> typically has a larger font-size to <body>, therefore the
'-4em' on h1 is larger than the 4em on <body>
body {margin-left: 4em}
h1 {margin-left: 0}
h1 will have the same indent as the body (margins are
relative to the parent element, not the screen)
Use of margins
- Use margins for
- indenting
- exdenting (using negative margins)
- adding space between paragraphs
- etc.
- When two margins meet vertically, only the larger is used (so the gap
between a heading and the following paragraph is the larger of the
heading's margin-bottom and the paragraph's
margin-top)
An Example
When two margins meet vertically, only the larger is used (so
the gap between a heading and the following paragraph is the larger of the
heading's margin-bottom and the paragraph's margin-top)
|
An Example
When two margins meet vertically, only the larger is used (so
the gap between a heading and the following paragraph is the larger of the
heading's margin-bottom and the paragraph's margin-top)
|
Padding: padding-top, -right, -bottom, -left
- These properties are similar to margins
- Examples of values: 0, 2em, 3pt, 1%, ...
- Initial: 0
- Percentages refer to parent element's width
Padding
- Negative values are not allowed
- Padding takes the colour of the element's background
- Example: padding-top: 1em
- Property padding works like margin, and has up to 4
values (TRBL):
padding: 1em 0em 2em 1em
Example
blockquote
{ margin: 2em;
background-color: yellow;
padding: 2em
}
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Borders: width, style and color
Borders can have a width, style and color.
For widths:
- Properties: border-top-width, -bottom-width, -right-width,
-left-width
- Example values: thin, medium, thick, 1pt, 1em, ...
- Initial: medium (but see border-style)
- Example: border-left-width: 1pt
Shorthand: border-width
- Property border-width can have up to 4 values, just like
margin and padding (TRBL)
- Example: border-width: 1pt 2pt
- So top, bottom=1pt,
- right, left= 2pt
border-style
- Property: border-style
- Values: none, dotted, dashed, solid, double, groove, ridge, inset,
outset
- Initial: none
- Sets value for all 4 sides! (But see border-top, border-right,
border-bottom, border-left)
dotted dashed solid double groove ridge inset outset
Shorthands: border-top, -right, -bottom, -left
One last border shorthand: border
Warning: border-style
If you set border-width, or border-color, and forget to set border-style,
since the default is 'border-style: none' you will see no border!
Always set border-style if you want a border.
Beware when using shorthands!
Better to be explicit.
Usage of borders
- Use borders for:
- Setting off text with a line each side
- Enclosing text in a box
- Putting a line under a paragraph
- Marking changed paragraphs with a line
- A border will often be too close to the text: use padding to
set it off from the text:
The End The End
height and width
The height and width of elements is normally determined by context or by
the element itself.
For instance, for text, the width is determined by the width of the
window, and the height by the amount of text.
Images have an inbuilt size.
You can change these defaults with the height and width properties.
- Property: height
- Values: auto, 100px, 15em, ... (no percentages)
- Initial: auto
width
- Property: width
- Values: auto, 100px, 15em, 50%, ...
- Initial: auto
- Percentages: refer to parent's width
- auto: calculated size, or intrinsic width for images.
- Example, to create a page of thumbnails:
img { width: 25% }
height is auto so will also scale to preserve aspect ratio
Auto values for box model
- Normally 'width' is 'auto'
- If no value is 'auto', margin-right will be set to 'auto'
Practical 2
- Use the file practical2.html; create and link to practical2.css
- Indent all text except for headings by some amount
- Limit the width of the page to some length
(note: bug in IE 5: setting width on <body> is not honoured)
- Make the headings white on blue, and right align them
- Make a stylesheet where only the headings are visible, and indented
according to their depth (h1, h2, etc)
Text properties: line-height
- The line-height is the distance between the base of one line, and the base of the next.
- Example values: normal, 1.2, 120%, 1.2em, 12pt, ...
- Initial: normal (browser specific)
- Better to use relative values
- If font-size is 10pt, then a line-height specified as 1.2, 120% or 12em
would result in a line-height of 12pt. The extra space is equally spread
above and below the line. (This paragraph has line-height: 100%, so should look a bit compressed)
Warning about line-height
- There is a difference in inheritance: a number (e.g. 1.2) is inherited
by the children, but in the case of other factors (120%, 12em), the
resulting value (e.g. 12pt) is inherited. If the child has a
different font-size, but no specified line-height, it may look wrong.
Use numbers.
body {font-size: 10pt; line-height: 1.2}
h1 {font-size: 20pt}
h1 has a line-height of 20pt x 1.2 = 24pt
body {font-size: 10pt; line-height: 1.2em}
h1 {font-size: 20pt}
h1 inherits the same line-height as body, which is 10pt x 1.2em = 12pt
text-indent
- This specifies the indentation of the first line of a block of text
- Example values: 0, 4em, 1%, ...
- Initial: 0
- Use negative values for exdenting a line.
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word-spacing, letter-spacing
- These are used to stretch or compress text by adding extra spacing
between letters or words
- Values: normal, 1%, 1px, ...
- Not widely implemented
Background properties: background-image
- Example values: none, url(back.gif)
- See background-repeat, background-position and background-attachment
for details of how it is displayed
- Works on any element, not just <body>!
background-position
- Specifies where background image is to be placed, or where repeating is
to start from
- Example values: 0% 0%, top left, center, any reasonable mixture of top,
bottom, center, left, right, ...
- Initial: 0% 0% (=top left)
background-repeat
- Specifies how background image is to be displayed
- Values: repeat, no-repeat, repeat-x, repeat-y
- no-repeat: just once at start position
- repeat-x: repeat horizontally both sides of the start position
- repeat-y: repeat vertically above and below start position
- repeat: repeat in all directions (tile the element)
- Initial: repeat
background-attachment
- Specifies if the background scrolls with the page, or stays put
- Values: scroll, fixed
- Initial: scroll
- Use for instance to put a logo or water-mark that remains visible when
the page is scrolled
Pseudo Classes: Anchors
a:link { color: blue }
a:visited { color: #f0f }
a:active { color: red }
a:link img { border-style: solid;
border-color: blue }
- CSS2, but useful. When the mouse is over an element:
a:hover {background-color: yellow}
Note on <a>
a {color: green}
a:link {color: blue}
This will colour <a name="..."> elements green, and
<a href="..."> elements blue.
Beware!
p {color: red}
a:link {color: blue}
<p><a href="...">Click here</a></p>
"Click here" will be blue.
Pseudo element:
first-line, first-letter
- There are also selectors to select the first line
and first letter of the formatted output:
p:first-line {font-variant: small-caps}
p:first-letter {color: red}
Float
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|
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|
Use of float
- Float works on any type of element, even text blocks!
- It can replace the use of tables for some layout
p.menu {float: left;
background-color: yellow;
margin-left: ...
<p class="menu">Menu items ...</p>
<p>Text ...</p>
Tjhds kdf jdfkjhs fkjdhfi i djhf jhfd ksfd sdjf isuzs ifsd l ojvcozx sf hi ihkshf iuhi ifsi iuf siu ojsorelk oisf oifk 9slkj iuhsfini kjfshiu isfiinf swjinsfi ujnhihnf ijnf iunfwe uhfi sifjh siuhk soh fsoi oidso oijso fijsoj osid psolknjlkzx osijfd oij sf lokjsfoiu oijsflk osi fsoijfs.
clear
- Allows an element to refuse floating elements one side or another
- Values: none, left, right, both
- Initial: none
- Example: h2 {clear: both}
Thth kjwehk kwkejt hkj twkjhk jrehtk jehrktj hkejrht kjherktj kj A Heading kwkejt hkj twkjhk jrehtk jehrktj hkeThth kjwehk kwkejt hkj twkjhk jrehtk jehrktj hkejrht kjherktj kj oiash fkjnskdf kn, sdf kjThth kjwehk kwkejt hkj twkjhk jrehtk jehrktj hkejrht kjherktj kj oiash fkjnskdf kn, sdf kjjrht. *** Thth kjwehk kwkejt hkj twkjhk jrehtk jehrktj hkejrht kjherktj kj oiash fkjnskdf kn, sdf kj kjherktj kj oiash fkjnskdf kn, sdf kj thth kjwehk kwkejt hkj twkjhk jrehtk jehrktj hkejrht kjherktj kj oiash fkjnskdf kn, sdf kj Thth kjwehk kwkejt hkj twkjhk jrehtk jehrktj hkejrht kjherktj kj oiash fkjnskdf kn, sdf kj
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Thth kjwehk kwkejt hkj twkjhk jrehtk jehrktj hkejrht kjherktj kj A Heading kwkejt hkj twkjhk jrehtk jehrktj hkeThth kjwehk kwkejt hkj twkjhk jrehtk jehrktj hkejrht kjherktj kj oiash fkjnskdf kn, sdf kjThth kjwehk kwkejt hkj twkjhk jrehtk jehrktj hkejrht kjherktj kj oiash fkjnskdf kn, sdf kjjrht. *** Thth kjwehk kwkejt hkj twkjhk jrehtk jehrktj hkejrht kjherktj kj oiash fkjnskdf kn, sdf kj kjherktj kj oiash fkjnskdf kn, sdf kj thth kjwehk kwkejt hkj twkjhk jrehtk jehrktj hkejrht kjherktj kj oiash fkjnskdf kn, sdf kj Thth kjwehk kwkejt hkj twkjhk jrehtk jehrktj hkejrht kjherktj kj oiash fkjnskdf kn, sdf kj
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Use of clear
Both of these images are at the start of the paragraph (in the source). The flower is first, then the star.
font-variant
- Values: normal, small-caps
- Uses a small-caps variant of the font
- Initial: normal
text-transform
- Values: none, uppercase, lowercase, capitalize
- Example: h1, h2, h3 {text-transform: uppercase}
- Initial: none
- Examples: none, uppercase,
lowercase, Capitalize
white-space
- Values: normal, pre, nowrap
- pre: use for <pre> like elements
- nowrap: text doesn't get wrapped
Remember: there is nothing inherent in the <pre> element that causes it to retain layout and output in a monospaced font: it is the styling that does that. You can change it.
list-style-type: examples
This is a single <ul> with different list-style-types applied to each <li>:
- disc
- circle
- square
- none
- decimal
- lower-roman
- upper-roman
- upper-alpha
- lower-alpha
list-style-position
- Values: inside, outside
- Default: outside
- Defines whether the bullet goes inside or outside the text box. As you may be able to see, this
line has a value for list-style-position of 'outside'.
- And if you compare this bulleted item with the one above, you should be able to see that
it has a value for list-style-position of 'inside'.
list-style
This is a shorthand
Selectivity of selectors
- !important wins
- browser → user → document
- id > class > no of tags in contextual selector
- pseudo-element = normal element,
pseudo-class = normal class
- Last specified wins if otherwise equal
- CSS rules win over HTML attributes (like bgcolor, align)
Practical 3
- Take a look at practical3.html, and example3.html
- Create a style sheet to make practical3.html look like example.3
- Hints:
- Use <span> where necessary in the HTML
- Use negative margins where necessary
- Use class="..." where necessary
- Resize the window to make sure it still works at different sizes.
Implementation
Already available in:
- Microsoft IE 3, 4, 5, 6
- Netscape 4, 6
- Opera 3, 4, 5, 6
- X-Smiles
- NetClue
- OmniWeb
- Mozilla
- Galeon
- Konqueror
- K-Meleon
- Escape
- Icab
- Openwave for phones
- Nokia phones
- Arachne
- Closure
- Emacs-w3
- Amaya
- Athena
- Closure
- HP ChaiFarer
- ICE
Level Compatibility
- All CSS1 rules are acceptable to CSS2 processors
- If a CSS1 browser comes across a CSS2 selector, it ignores the whole
rule
- If a CSS1 processor comes across a CSS2 property or value, it ignores
only the declaration.
Ignore rule: *[width] {font-size: 10pt; color: blue}
Ignore declaration: p {overflow: hidden; color: blue}
Ignore declaration: h2 {display: run-in; color: blue}
CSS2 and 3
Later areas of work include:
- Speech
- Layout
- Fuller control
- Printing
- ...
CSS2
- Aural style sheets:
h1 { voice-family: male;
pitch: low; speech-rate: slow}
- inherit as value for all properties
- Media types
@media print { body {font-size: 10pt} }
@media screen { body {font-size: 12pt} }
@media projection { body {font-size: 20pt} }
h1 {font-size: 2em}
- Control of tables
- Page layout
- Bi-directional text
- Web fonts
CSS3
- Printing
- Multicolumn
- Headers and footers
- ...
Where?
The definition of CSS1 can be found at:
http://www.w3.org/TR/REC-CSS1
The definition of CSS2 is at
http://www.w3.org/TR/REC-CSS2/
CSS resources can be found at www.w3.org/style/css
Future Markup
- HTML was designed for just one sort of document (scientific reports),
but is now being used for all sorts of different documents
- You could use SGML to define other sorts of document, but SGML is
notoriously hard to fully implement
XML
- XML is a W3C effort to simplify SGML
- It is a meta-language, a subset of SGML
- One of the aims is to allow everyone to invent their own tags
- DTD is optional: a DTD can be inferred from a document
Consequences
- The requirement of being able to infer a DTD from a document has an
effect on the languages you can define:
- Closing tags are now required
<LI>....</LI> <P>....</P>
- Empty tags are marked specially
<IMG SRC="pic.gif"/> <BR/> <HR/> (or
<HR></HR> etc)
So do we still need HTML?
- XML is still a meta-language
- There is still a perceived need for a base-line mark-up
- HTML has some useful semantics, both implied and explicit (search
engines gladly use it, for instance)
HTML as XML application
- Clean up (get rid of historical flotsam)
- Modularise – split into separate parts
- Allows other XML applications to use parts
- Allows special purpose devices to use subset
- Add any required new functionality (forms, better event handling,
Ruby)
Differences HTML:XHTML
- Because of the difference between SGML and XML, there are some
necessary differences, for instance:
- Use lower case: <p> not <P>
- Attributes are always quoted:
<th colspan="2">
- Anchors use id attribute not name (and not just on
<a> by the way):
<a id="index"> <p id="top">
Example
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head><title>Virtual Library</title></head>
<body>
<p>Moved to <a href="http://vlib.org/">vlib.org</a>.
</p>
</body>
</html>
Namespaces
<html xmlns="http://www.w3.org/1999/xhtml">
<head><title>A Math Example</title></head>
<body>
<p>The following is MathML markup:</p>
<math xmlns="http://www.w3.org/TR/REC-MathML">
<apply><log/><logbase><cn> 3 </cn> </logbase>
<ci> x </ci>
</apply>
</math>
</body></html>
Transition
- XHTML 1.0 has been carefully designed to make use of 'quirks' in
existing HTML browsers
- Use of a small number of guidelines allows XHTML to be served to HTML
browsers
Versions of XHTML
There are now several versions of XHTML in use:
- XHTML 1.0: 'Legacy-compatible' version.
- XHTML 1.1: Cleaned up version of XHTML 1.0 Strict
- XHTML Basic: For small devices. About to appear in many WAP 2 phones.
There is also a special version for TVs in preparation, as well as XHTML 2.0, with many new features.
Result
- XML with related technologies gives you the freedom to define and
deliver your own document types
- HTML is still needed as a base-line markup
- The new HTML gives a transition path to the future
- Since there is no built-in presentation semantics any more, CSS is
essential
Reminder: Using style sheets with XML
For XML use a processing instruction:
<?xml-stylesheet type="text/css"
href="your-filename.css"?>
Put before first element of the document
Practical 4
- File practical4.xml is an xml document. Take a look.
- As you can see, XML has no pre-defined presentation.
- Add a link to a style-sheet file from the document.
- Start off with an empty CSS file; how does the document look now?
- Now start defining CSS rules for the elements so that the document
begins to look reasonable.
Overview of properties, with examples and
defaults
- font-*:
family (Futura, ..., serif, sans-serif, cursive, fantasy,
monospace)
style (normal, italic,
oblique)
variant (normal, small-caps)
weight (normal, bold, bolder, lighter,
100, ..., 400, ..., 900)
size (10pt, 120%, small, medium, large, smaller, larger,
...)
- color (red, ..., #f00,
#ff0000, rgb(255,0,0), rgb(100%, 0, 0), ...)
- background-*:
color (transparent, red, black, white,
gray, silver, red, maroon,
yellow,olive,green,lime,blue,navy,purple,aqua,fuschia,teal,...)
image (none, url(back.gif))
repeat (repeat, no-repeat, repeat-x,
repeat-y)
attachment (scroll, fixed)
position (0% 0%, top left, center,
center left, bottom right, ...)
- line-height (normal, 120%,
...)
- word-spacing, letter-spacing (normal, 1%, 1px,
...)
- vertical-align (baseline, sub, super,
10%, top, text-top, middle, ...)
- text-*:
decoration (none, underline, overline,
line-through, blink)
transform (none, uppercase, lowercase,
capitalise)
align (justify, left, right, center)
indent (0, 4em, ...)
- display (block, inline, list-item, none)
- white-space (normal, pre,
nowrap)
- list-style*:
type (disc,circle,square,decimal,none,lower-roman,lower-alpha,
... )
image (url(sphere.gif), none)
position (inside, outside)
list-style (type position
<url>)
Overview of box properties
- margin-*: top, right, bottom, left (0, auto, 2em, 3pt, 1%, ...)
- padding-*: top, right, bottom, left (0, 2em, 3pt, 1%, ...)
- border-*:
width4 (thin, medium, thick,
2pt, ...)
style (none, dotted, dashed, solid,
double, ...)
color4 (...)
top, right, bottom, left (width style
colour)
top-width, bottom-width, right-width, left-width (medium, ...)
- margin4 (top right bottom
left)
- padding4 (top right bottom
left)
- border (width style color)
- height, width (auto, 100px, 15em,
50%, ...)
- float (none, left, right)
- clear (none, left, right,
both)