Web Usability with Style Sheets (original) (raw)

Agenda

The day is split into four blocks, each of 90 minutes.

Each block consists of about 45 minutes 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

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 was 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. He is co-author of (amongst other things) HTML 4, CSS, XHTML and XForms.

Steven is also Editor-in-Chief of ACM/interactions.

Objectives

HTML has for too long, and incorrectly, been 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, limit the sorts of devices that may be used to view websites, 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.
By not coding device-dependent presentations in the HTML pages are viewable on a wider range of devices.
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, showing in passing 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. In particular, there are only three images used (to demonstrate the use of images): a star, and two versions of a flower. All other things that look like images are in fact just styled with CSS.

It should go without saying that to properly appreciate this document, you have to view it with a browser with good CSS support.

If you can see this text, your browser apparently does not support CSS.

Course Plan

Part 1

Introduction, basic CSS: selectors, fonts, colours; Practical

Part 2

Intermediate-level stuff: advanced selectors, inheritance, margins, borders, padding; Practical

Part 3

Advanced stuff: text properties, background, positioning; Practical

Part 4

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,

defines a heading without specifying how it should look.
- ...
specifies a list of items.
These classifications often have semantic significance. and were mistakes, use and 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 and
These do specify how the item should look, and have no inherent semantics; Microsoft also followed suit.
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

Motivation

Csszengarden.com is a website with essentially one HTML page.

And hundreds of beautiful, breathtaking CSS stylesheets applied to that one page.

Is uses very simple HTML: div, h1, h2, h3, span, p, ul/li, a, acronym

As you look at each presented page, you have to keep repeating to yourself: this is the same HTML page.

Butterfly

Post

focus

gemination

party

worm

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
Documents are smaller: less bandwidth
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, 7 and its Mozilla-based relatives
- Opera 3.5, 4, 5, 6, 7
While the quality of the support for CSS on these browsers varies, though is continually improving, you never need to use the 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:

**** ...

Inline style is also possible

You can also put your style sheets in the head of your HTML document:

****

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:

Stop!

This is bad practice, and undoes many of the advantages of CSS.

Doesn't (necessarily) work for XML.

Warning about HTML:

is not the same as
!
Don't do this:
The Title
This is the first paragraph
And this is the second
But this:
The Title

This is the first paragraph

And this is the second
Your CSS will work better, and new versions of HTML require it anyway.

Warning about old browsers

CSS implementations are now quite good, but older browsers had a variety of mistakes. Unfortunately, some browser manufacturers want to offer backwards compatibility with those buggy old browsers. So they have two modes: compliant mode, and legacy mode.

To decide which mode to use they look at the document.

Legacy and compliant modes

For XML it is always in compliant mode
For HTML it is compliant mode if you include a DOCTYPE at the top of the document, for instance:

So if you want your CSS to work right, always include a DOCTYPE at the head of your document.

Structure of CSS1

CSS has rules consisting of selectors and blocks;
Blocks are a series of declarations between curly brackets, separated by semicolons:
H1 { font-family: helvetica, sans-serif;
font-weight: bold }
Declarations consist of a property followed by a value
(declarations may also be empty):
font-size: 10pt

Comments

Comments are expressed between /* and */
Example:
/* This is a comment */

Basic Selectors

Basic selectors are just element names
- H1
- BODY
- P
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

Warning about HTML: case

HTML is case-insensitive. You can write
Title
or
Title
Therefore, you can write selectors either as
H1 {font-weight: bold}
or
h1 {font-weight: bold}
Newer versions of HTML are case sensitive, so specify your selectors in lower case

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.

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. )
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

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

Lengths

Relative:

Ems: 4em
X height: 1ex
Percentages: 120%

Absolute:

Pixels: 12px
Inches: 0.5in
Cm: 2.5cm, Mm: 25mm
Points: 10pt
Picas: 2pc (1pc = 12pt)

Warning about font sizes

Don't use pixels for font sizes, because you don't know the resolution of the screen that anyone is using.

For instance, font-size: 12px will give you

12 point on a 72dpi screen
9 point on a 96dpi screen
6.9 point on a 125dpi screen

Similarly, avoid using point sizes as well:

Many machines are not properly set up (the operating system doesn't know the screen resolution)
Many people can't see text below a certain size, and so increase the base font-size

Respect these people: try to use relative font sizes. Use font-size: 100% for paragraph text, font-size: 120% or so for headings, font-size: 80% for copyright statements, etc.

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

Make a stylesheet that gives elements a yellow background colour, and makes elements be white text on a black background.

Class Selectors

If an element has a class attribute, you can select on it
In the CSS:
p.important { color: red }
In the HTML:
Do not phone before 09:00!
or all "important" elements regardless of type:
.important { color: red }

Use of HTML: span

Use the element as a carrier of class information:
Do not cross
If you want such text to be styled in some way on non-CSS browsers as well, use or instead:
Do not cross
Do not cross
An element can have several classes:
...

Advice: use class names that describe the purpose, not the presentation. For instance, use class="important", not class="red".

ID Selectors

You can select any element with a particular ID tag with #:

#dateline { .... }

Monday 12th May ... * or a particular type of element with an ID: h2#index { .... }

Index

Use an ID selector to document that there can only be one in the document, while there can be any number of elements using the same class.

Contextual Selectors

These allow you to address the nesting of the document:

h1 { font-weight: bold } em { font-style: italic }

Now is the time!

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; color: red }
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), but all selectors apply. So since the first ul li rule sets the colour to red, all nested li's are red too.

Inheritance

Note that in the following the element is also blue. It is_inherited_ by the element.
h1 { color: blue }
Now is the time
_Now_ is the time
Many properties are inherited, but some are not, such as borders:
Now is the time
If the border-style were inherited by the , you would get:
Now is the time

Use of HTML: div

Like for inline text, use
to carry class or ID information for larger blocks:

Chapter 2

It was dark. ...
... **
** div.chapter h2 {font-family: pembo, cursive}

display

Some elements (like , ) are inline. Others (like
,
) 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 (
in HTML) (more properties later)
none: the element is not displayed at all.
Initial value: not important for HTML; different for CSS1 and CSS2, sonever assume a default!

Example of display: none

In the CSS:

.notcss {display: none}

In the HTML:

Your browser doesn't support CSS

Example of display: none

You can use display: none with different stylesheets, to make different parts of the document visible. E.g. one stylesheet can show deletions with the text struck through:

del { text-decoration: line-through }

another can make the deletions not visible:

del { display: none }

NB with:

body {display: none} h1 {display: block}

the h1's are still invisible, since thewhole body is invisible

text-align

Values: justify, left, right, center
Applies to blocks (i.e. elements with display: block or list-item)
Initial: not defined

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Box model

All elements have this box model.
The margin's colour is transparent
The border's colour is by default the same as the text of the content, but can be set separately
The padding has the same colour as the background colour of the content

height and width properties

Margin
Border
Padding
Content	Height



Width

The 'height' and 'width' properties of an element affect the height and width of the 'content' part
So if you set width to 4em, padding to 3em, border to 2em, and margin to 1em, the whole box will be (4 + 2×3 + 2×2 + 2×1) = 16em wide. (But see note later on 'auto' values).

Note major bug in early versions of IE, where width affected the whole box. This still shows up in modern IE if you forget the DOCTYPE.

Box model: margin, border, padding

All three are changeable:
h1 { margin: 2pt;
border-width: 4pt;
border-style: dotted;
padding: 3pt}
Also per part:
h1 { border-top: 4pt solid red}
also -left, -right and -bottom

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 the 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}
typically has a larger font-size to , therefore the '-4em' on h1 is **larger** than the 4em on
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)

Shortcuts: margin

There are a number of shortcuts for some properties. For margins you can set all 4 sides at once:
margin: 1em (sets all 4 to 1em)
margin: 0 1em 0 2em
The four values go clockwise and set top right bottom left respectively (TRBL: mnemonics treble, tribal, terrible, true-blue)
Missing values are obtained from the opposite side: "margin: 0 1em" is the same as "margin: 0 1em 0 1em"

Use of margins

Use margins for indenting:
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Invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua.
exdenting (using negative margins):
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adding space between paragraphs
etc.

When vertical margins meet

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 of padding

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

border-color

Property: border-color
Values: one to four colours (see color property)
Initial: whatever value the color property has for this element
Four values work like margin (etc): TRBL
Example:
border-color: red white blue
(left side is thus also white)

Shorthands: border-top, -right, -bottom, -left

Values: width style colour
Example:
p.note {border-left: medium solid black}
Initial: as individual properties
Values may be in any order (border-top: thin red 1pt)
Any of the three values may be left out (but see warning later):
border-top: thin blue

One last border shorthand: border

Property: border
Values: width style color
Values may be in any order, and any may be omitted (but see warning)
Sets all 4 sides
Example
p.warning {border: solid thick red}

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.

Warning about using shorthands

Border and border-top (etc) also set the colour, so with:
blockquote {color: black;
border: red medium solid;
border-left: dotted }

even though the colour isn't mentioned in the border-left property, it is there! And its value is the value of color: therefore the left border will be black.

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'

Example

mmmmm

with

div {margin: 0.5em 1em; border: thin black solid}

gives:

Example (contd)

Setting respectively inner, middle and outer to width: 9em gives:

Practical 2

Make a stylesheet that indents all text except headings.

Make a stylesheet that hides all text except headings. Indent headings according to their importance (don't indent

; indent

a little;

a little more, 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 1.2em 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.If in doubt, 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-decoration

Values: none, or any combination of: underline, overline, line-through, blink
Initial: none
Not all browsers implement blink.
Example:
a {text-decoration: underline}
underline, overline, line-through, mixture

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 tostretch a number of wordsor compress a number of words by adding extra spacing between letters or words
Values: normal, 1px, 0.1em, ...
Not widely implemented

vertical-align

For effects like subscript and superscript
Values: baseline,sub, super, top, text-top, middle, bottom, text-bottom
Values: (of line height; this is 100%)
Initial: baseline
Only trust baseline, sub, and super at present
Example:
sub {vertical-align: sub}

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 !

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)
This example is bottom right

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

Technique: Images for headlines

All too often Websites use images for major headings. This causes some problems:

Google doesn't see the text, nor know it's a heading
Other software doesn't know it's a heading
Causes problems with accessible software
Doesn't scale on the screen
Doesn't work with browsers that don't handle images.

However, there is a technique that gives you the best of both worlds: put the text in the HTML and override it with an image in the CSS

Images for headlines

In the HTML, use a heading, with the text in a span:

Images for headlines

In the CSS, turn off the span:

h1 span {display: none}

and add a background image to the h1:

h1 { background-image: url(text.gif); background-repeat: no-repeat; background-position: 50% 50% height: 80px; width: 80px; }

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 {color: green} a:link {color: blue}

This will colour elements green, and
elements blue.

Beware!

p {color: red} a:link {color: blue}

Click here

"Click here" will be blue.

Pseudo element:

first-line, first-letter

Note there are also selectors to select the first line
and first letter of the formatted output:

p:first-line {font-variant: small-caps; color: blue} p:first-letter {font-size: 200%; color: red}

Not widely implemented

font-variant

Values: normal, small-caps
Uses a small-caps variant of the font
Initial: normal

Float

Move elements relative to the parent
Values: none, left, right
Example. Logo always on the side of the window:
img.logo {float: right}
img.logo {float: left}
Initial: none

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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; ...

Menu items ...

Text ...

Technique: multi-columns using float

div.col { width: 31%; text-align: justify; padding-left: 1%; padding-right: 1%; border-left: solid 1px black; margin: 1em 0; float: left; } div.col.first {border-style: none}

An example of columns

Here is an example of columns using CSS:

This is a div of class = "first col". Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna.

This is a div of class = "col". Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna.

And then back to single column format after the divs.

clear

Allows an element to refuse floating elements one side or another
Values: none, left, right, both
Initial: none
Example: h2 {clear: left}

poppy Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor.

A Heading

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A Heading

Use of clear

Both of the images are at the start of the paragraph (in the source). The flower is first, then the star; the left example has img {float: left} and the right has img {float: left; clear: left}:

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text-transform

Values: none, uppercase, lowercase, capitalize
Example: h1, h2, h3 {text-transform: uppercase}
Initial: none
Examples: none, uppercase, lowercase, Capitalize

font

This is a shorthand for font-style, font-variant, font-weight, font-size, line-height, font-family
Example:
p.abstract
{font: medium italic 10pt/12pt
times, serif }

white-space

Values: normal, pre, nowrap
pre: use for
```
 like elements
```
nowrap: text doesn't get wrapped

Remember: there is nothing inherent in the

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

Values: disc, circle, square, decimal, lower-roman, upper-roman, lower-alpha, upper-alpha, none
Applies to elements with display: list-item
Example:
ul li {list-style-type: disc}
ul ul li {list-style-type: circle}
ol li {list-style-type: decimal}

list-style-type: examples

This is a single

:
- disc
- circle
- square
- none
- decimal
- upper-roman
- lower-roman
- upper-alpha
- lower-alpha
list-style-image
- Example values: none, url(star.gif)
- Allows you to define your own sort of bullets
- Example:
  ul.special {
  list-style-image: url(ball.gif)}
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
- Values: type style position
- Example:
  ul.special {
  list-style: url(ball.gif) inside}
Cascading
- A browser has an implicit default style sheet
- The user may have a preferences style sheet
- Browser default → Reader preferences → Document
- You can combine several style sheets (= cascading)
  @import url(house.css);
  body { font-size: 30pt }
- You can override with !important:
  body {color: black !important;
  background-color: white !important}
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)
Optional Stylesheets

Media: all, screen, print, projection, handheld, tv, tty, aural, braille, embossed.

Also:

Practical 3
Here is a document styled with HTML and images.

Do some of the obvious parts with CSS (as much as you have time for).

Implementation
Already available in:
- Microsoft IE 3, 4, 5, 6
- Netscape 4, 6, 7
- Opera 3, 4, 5, 6, 7
- X-Smiles
- NetClue
- OmniWeb
- Mozilla, Galeon, Firebird, K-Meleon, Chimera, ...
- Konqueror
- Safari
Implementation
- Escape
- Icab
- Millions of mobile phones
- Arachne
- 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
- ...
Selectors
More selectors, such as:
- *: any element
- E > F: selects any element F that is a child of E
- E:first-child: selects any E that is the first child of its parent (To select the first child of an element E use "E > :first-child")
- E + F: any F that directly follows an E
- E[att]: any E that has attribute att
- E[att="value"]: where att has exactly the value
- E[att~="value"]: where one of the words of att is the value
Features
- Embedded media rules: all, screen, print, projection, handheld, tv, tty, aural, braille, embossed
  @media print { body {font-size: 10pt} }
  @media screen { body {font-size: 12pt} }
  @media projection { body {font-size: 20pt} }
  h1 {font-size: 2em}
- inherit as value for all properties
- Control of tables
- Page layout
- Bi-directional text
- Web fonts
- Aural style sheets: h1 { voice-family: male; pitch: low }
More features
- Generated content, and control over counters
- Text shadows
- Borders and padding properties fixed up; outlines
- display: new values
- Absolute and relative positioning of elements; z-index for overlapping
- Overflow control and clipping
- Font stretching and adjusting
- System colours, more units, more to font, list-style-types
- + details
Overflow
Values: visible, hidden, scroll, auto, inherit
Default: visible
- Visible: show even if it doesn't fit
- Hidden: hide what doesn't fit
- Scroll: use scroll bars regardless
- Auto: use scrollbars if needed
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Position
Values: static, relative, absolute, fixed, inherit
Default: static
- Static: not positioned
- Relative: positioned relative to current position (like sub/superscripting)
- Absolute: positioned absolutely in the document (relative to closest enclosing absolutely positioned box, or otherwise the whole document)
- Fixed: positioned absolutely on the screen
Uses properties:
- top, bottom, left, right: the offset of the positioned box from the position is is being positioned against.
Technique – a fixed list of links
See example. HTML:

Links

Home Away ...

And then in the CSS:

.nav { position: fixed; top: 0; right: 0; width: 6em; ...} .nav a {display: block}

Technique: Hover pop-ups
ExampleAn example of popup text controlled entirely by CSS

This contains markup like

ExamplePopup text here

and rules like

a.popup span {display: none} a.popup:hover span { display: block; width: 10em; background-color: yellow; border: dotted black thin; position: relative; left: 100px;}

Generated content
You can generate content that isn't in the document.

For instance, this slide does not have the initial "CSS2: " in the header, but a rule that says

h2.CSS2:before {content: "CSS2: "}

There is also a ":after".

Numbering
In the printed version of these slides, each slide has bene given a number.

This is done using rules like:

div.slide h2 {counter-increment: slide} div.slide h2:before{ content: counter(slide) " "}

CSS3
- Printing
- Multicolumn
- Headers and footers
- More media queries
- ...
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
- ....
Empty tags are marked specially

(or
etc)

Consequences 2

CDATA sections must be marked as such (if they contain "<", "&" etc.):

Consequence of XML
- Anyone can now design a (Web-delivered) language
- CSS makes it viewable
  **Steven Pemberton** **CWI** **Kruislaan 413** **1098 SJ** **Amsterdam**
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:
  not
- Attributes are always quoted:
- Anchors use id attribute not name (and not just on by the way):
Example
Virtual Library
Moved to vlib.org.

Namespaces
A Math Example
The following is MathML markup:
**** ** 3 ** ** x ** **** ****
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
Examples of Guidelines
- Use space before / of empty elements:
- Use name= and id= on :
  ...
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. Now in many WAP 2 phones.
There are also versions for TVs and printers 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:

Put before first element of the document

Practical 4: RSS
An RSS documentis an XML document that contains elements like this:

<**item** rdf:about="" title="undefined" rel="noopener noreferrer">http://www.w3.org/News/2004#item155"> <**title**>W3C Celebrates Ten Years Leading the Web</**title**> <**description**>This year, W3C celebrates its tenth anniversary. ... </**description**> <**link**>http://www.w3.org/News/2004#item155</**link**> <**dc:date**>2004-10-07 </**item**>

Write a stylesheet to make such a document readable.

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 )
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)
Web Resources for CSS, XML and XHTML
- A list of known books about CSS, online resources, supporting browsers, and editors: http://www.w3.org/Style/CSS.
- The CSS1 Recommendation: http://www.w3.org/TR/REC-CSS1
- The CSS2 Recommendation: http://www.w3.org/TR/REC-CSS2/
- A CSS1 Quick reference: http://www.cwi.nl/~steven/www/css1-qr.html
- XHTML: http://www.w3.org/TR/xhtml1/ with more information at http://www.w3.org/Markup
- XML: http://www.w3.org/TR/REC-xml with more information at http://www.w3.org/XML/
- An excellent book on CSS2, is by two of its creators, Håkon Lie and Bert Bos. It is Cascading Style Sheets: Designing for the Web, published by Addison-Wesley.
- Validate your CSS: http://jigsaw.w3.org/css-validator/
- Validate your HTML and XHTML: http://validator.w3.org/
- Tidy up your HTML, making it more amenable for CSS, and convert it to XHTML 1.0: http://www.w3.org/People/Raggett/tidy/
- Test your browser for CSS compliance: http://www.w3.org/Style/CSS/Test/
- A set of style sheets for HTML designed by a graphic-designer: http://www.w3.org/StyleSheets/Core/
- How well (or badly) browsers implement CSS, feature by feature: http://www.webreview.com/style/css1/charts/mastergrid.shtml
- Workarounds for browser bugs: http://css.nu/pointers/bugs.html
- Google's directory of resources: http://directory.google.com/Top/Computers/Programming/Internet/CSS/.
- The 'House of Style': http://www.westciv.com/style_master/house/
- A webzine of standards-based web-building techniques: http://www.alistapart.com/stories/.
- Standards evangelism: http://www.webstandards.org/.
- Some examples of CSS-based sites: W3C,Wired, webstandards.org, A List Apart, a Lycos redesign at http://jscript.dk/lycos/2/, XHTML2 at http://w3future.com/weblog/gems/xhtml2.xml.
Quick Reference to Cascading Style Sheets, level 1
This version is based on:

http://www.w3.org/TR/REC-CSS1

Latest version:

http://www.w3.org/TR/WD-css1.html

Author:

Steven Pemberton (Steven.Pemberton@cwi.nl)

Syntax
a b c

a is followed by b is followed by c, in that order.

a | b

either a or b must occur

a || b

either a or b or both must occur, in any order

[a b]

brackets, used for grouping

a?

a is optional

a*

a is repeated 0 or more times

a+

a is repeated 1 or more times

a{1,4}

a is repeated at least once and at most 4 times.

Juxtaposition is stronger than the double bar, and the double bar is stronger than the bar. Thus "a b | c || d e" is equivalent to "[ a b ] | [ c || [ d e]]".

Definitions
Block-level elements

an element which has a line break before and after (e.g.
,
)

Replaced element

An element which is replaced by content pointed to from the element. E.g., .

Properties
In each definition
- the default value is shown in bold, or given separately
- values apply to all elements unless otherwise stated
- properties are inherited unless the property name is marked with a star "*".
5.2 Font properties
5.2.2 font-family

[[ | ],]* [ | ]
Initial: UA specific

serif | sans-serif | cursive | fantasy | monospace

5.2.3 font-style

normal | italic | oblique

5.2.4 font-variant

normal | small-caps

5.2.5 font-weight

normal | bold | bolder | lighter | 100 | 200 | 300 | 400 | 500 | 600 | 700 | 800 | 900

5.2.6 font-size

| | |
Initial: medium
Percentage values: relative to parent element's font size

xx-small | x-small | small | medium | large | x-large | xx-large

larger | smaller

5.2.7 font

[ || || ]? [ / ]?
Initial: not defined for shorthand properties
Percentage values: allowed on and

5.3 Color and background
5.3.1 color
_Initial:_ UA specific
5.3.2 background-color*

| transparent

5.3.3 background-image*

| none

5.3.4 background-repeat*

repeat | repeat-x | repeat-y | no-repeat

5.3.5 background-attachment*

scroll | fixed

5.3.6 background-position*

[ | ]{1,2} | [top | center | bottom] || [left | center | right]
Applies to: block-level and replaced elements
Initial: 0% 0%
Percentage values: refer to the size of the element itself

5.3.7 background*

|| || || ||
Initial: not defined for shorthand properties
Percentage values: allowed on

5.4 Text properties
5.4.1 word-spacing

normal |

5.4.2 letter-spacing

normal |

5.4.3 text-decoration*

none | [ underline || overline || line-through || blink ]
Inherited: no, but see clarification below

5.4.4 vertical-align*

baseline | sub | super | top | text-top | middle | bottom | text-bottom |
Applies to: inline elements
Percentage values: refer to the 'line-height' of the element itself

5.4.5 text-transform

capitalize | uppercase | lowercase | none

5.4.6 text-align

left | right | center | justify
Applies to: block-level elements
Initial: UA specific

5.4.7 text-indent

|
Applies to: block-level elements
Initial: 0
Percentage values: refer to parent element's width

5.4.8 line-height

normal | | |
Percentage values: relative to the font size of the element itself

5.5 Box properties
5.5.1 margin-top*

| | auto
Initial: 0
Percentage values: refer to parent element's width

5.5.2 margin-right*

| | auto
Initial: 0
Percentage values: refer to parent element's width

5.5.3 margin-bottom*

| | auto
Initial: 0
Percentage values: refer to parent element's width

5.5.4 margin-left*

| | auto
Initial: 0
Percentage values: refer to parent element's width

5.5.5 margin*

[ | | auto ]{1,4}
Initial: not defined for shorthand properties
Percentage values: refer to parent element's width

5.5.6 padding-top*

|
Initial: 0
Percentage values: refer to parent element's width

5.5.7 padding-right*

|
Initial: 0
Percentage values: refer to parent element's width

5.5.8 padding-bottom*

|
Initial: 0
Percentage values: refer to parent element's width

5.5.9 padding-left*

|
Initial: 0
Percentage values: refer to parent element's width

5.5.10 padding*

[ | ]{1,4}
Initial: 0
Percentage values: refer to parent element's width

5.5.11 border-top-width*

thin | medium | thick |

5.5.12 border-right-width*

thin | medium | thick |

5.5.13 border-bottom-width*

thin | medium | thick |

5.5.14 border-left-width*

thin | medium | thick |

5.5.15 border-width*

[thin | medium | thick | ]{1,4}
Initial: not defined for shorthand properties

5.5.16 border-color*

{1,4}
Initial: the value of the 'color' property

5.5.17 border-style*

none | dotted | dashed | solid | double | groove | ridge | inset | outset

5.5.18 border-top*

|| ||
Initial: not defined for shorthand properties

5.5.19 border-right*

|| ||
Initial: not defined for shorthand properties

5.5.20 border-bottom*

|| ||
Initial: not defined for shorthand properties

5.5.21 border-left*

|| ||
Initial: not defined for shorthand properties

5.5.22 border*

|| ||
Initial: not defined for shorthand properties

5.5.23 width*

| | auto
Applies to: block-level and replaced elements
Percentage values: refer to parent element's width

5.5.24 height*

| auto
Applies to: block-level and replaced elements

5.5.25 float*

left | right | none

5.5.26 clear*

none | left | right | both

5.6 Classification
5.6.1 display*

block | inline | list-item | none

5.6.2 white-space

normal | pre | nowrap
Applies to: block-level elements

5.6.3 list-style-type

disc | circle | square | decimal | lower-roman | upper-roman | lower-alpha | upper-alpha | none
Applies to: elements with 'display' value 'list-item'

5.6.4 list-style-image

| none
Applies to: elements with 'display' value 'list-item'

5.6.5 list-style-position

inside | outside
Applies to: elements with 'display' value 'list-item'

5.6.6 list-style

|| ||
Applies to: elements with 'display' value 'list-item'
Initial: not defined for shorthand properties

6.1 Length units

[+|-]?

+[.*]?

|

mm | cm | in | pt | pc

em | ex | px

6.2 Percentage units

%

6.3 Color units

|

aqua | black | blue | fuchsia | gray | green | lime | maroon | navy | olive | purple | red | silver | teal | white | yellow

# |
# |
rgb(, , ) |
rgb( , )

6.4 URL

url()

Web Usability with Style Sheets (original) (raw)

Agenda

Block 1

Block 2

Block 3

Block 4

About the Instructor

Objectives

Course Plan

HTML and SGML

Contamination

CSS

Motivation

Separating Content and Presentation: Author Advantages

Separating Content and Presentation: Webmaster Advantages

Separating Content and Presentation: Reader Advantages

Separating Content and Presentation: Implementor Advantages

Levels

Check your log files!

Why is Usability Important for Websites?

Why is CSS good for usability?

Using CSS

Inline style is also possible

Style sheets for XML

HTML Style Attributes

Warning about HTML:

The Title

The Title

Warning about old browsers

Legacy and compliant modes

Structure of CSS1

Comments

Basic Selectors

Warning about HTML: case

Title

Title

Examples

All matching rules apply

Styling text

font-size

Warning about 'initial values'

Lengths

Warning about font sizes

font-weight

font-style

font-family

Colours: color and background-color

Practical 1

Class Selectors

Use of HTML: span

ID Selectors

Index

Contextual Selectors

Now is the time!

Examples of contextual selectors

Inheritance

Now is the time

Use of HTML: div

Chapter 2

display

) are blocks. The display property specifies this for the presentation

Example of display: none

Example of display: none

text-align

Box model

height and width properties

Box model: margin, border, padding

Margins: margin-top, -right, -bottom, -left

Warnings about use of margins

typically has a larger font-size to , therefore the '-4em' on h1 is **larger** than the 4em on

Shortcuts: margin

Use of margins

When vertical margins meet

An Example

An Example

Padding: padding-top, -right, -bottom, -left

Padding

Example of padding

Borders: width, style and color

Shorthand: border-width

typically has a larger font-size to , therefore the '-4em' on h1 is larger than the 4em on