TIP 43

Valid CSS and Accessibility

CSS, or Cascading Style Sheets, is a 'language' that website designers use to develop the style, look and feel of layout, text and colours on a website page.

Used properly, CSS can be used to Separate design from content, making websites easier to use and ultimately, maintain. It can also help with download times as the CSS is downloaded only once and held in browser cache.

A good (the best?) website development technique is to build your pages using HTML and link this page to what is called an external css file that controls all elements of style on the site. Link the stylesheets in your <HEAD> like so:

<link rel="stylesheet" href='../style1/css/screen.css' type="text/css">

What is CSS?

CSS means 'Cascading Style Sheets'
CSS Styles define how to display HTML elements
CSS Styles are normally stored in 'External' CSS Style Sheets
CSS Styles were added to HTML 4.0
External Style Sheets can save website designers a lot of time and effort
Multiple CSS style definitions will cascade into one

What Is CSS For?

HTML tags were originally designed to define the content of a document. They were supposed to say "This is a header", "This is a less important header ", "This is a paragraph ", by using tags like <h1>, <h2>, <p>, and so on. The layout of the document was supposed to be taken care of by the browser, without using any formatting tags.

Netscape and Internet Explorer continued to add new HTML tags and attributes (like the <font> tag and the color attribute) to the original HTML specification. It soon became more and more difficult to create Web sites where the content of HTML documents was clearly separated from the document's presentation layout.

To solve this problem, the World Wide Web Consortium (W3C) - the non profit, standard setting consortium, responsible for standardizing HTML - created STYLES in addition to HTML 4.0.

All major browsers support Cascading Style Sheets, although some, handle them slightly differently, which an be a pain to the website designer!

Cost Effective Website Design With CSS

CSS defines how HTML elements are to be displayed. CSS Styles are normally saved in external .css files. External style sheets enable you to change the appearance and layout of all the pages in your Web, just by editing one single CSS document!

CSS allows website developers to control the style and layout of multiple web pages all at once. As a Web developer you can define a style for each HTML element and apply it to as many website pages as you want. To make a site-wide change, simply change the style, and all elements in the website are updated automatically.

Multiple Styles Will Cascade Into One Style

Style sheets allow style information to be specified in many ways. Styles can be specified inside a single HTML element, inside the <head> element of an HTML page, or in an external CSS file. Even multiple external style sheets can be referenced inside a single HTML document.

Cascading Order of CSS

CSS styles will "cascade" into a style by the following rules, where number four has the highest priority:

Browser default
External style sheet
Internal style sheet (inside the <head> tag)
Inline style (inside an HTML element)

So, an inline style (inside an HTML element) has the highest priority, which means that it will override a style declared inside the <head> tag, in an external style sheet, or in a browser (a default value).

CSS Syntax

The CSS syntax is made up of three parts: a selector, a property and a value:

selector {property: value}

The selector is normally the HTML element/tag you wish to define, the property is the attribute you wish to change, and each property can take a value. The property and value are separated by a colon, and surrounded by curly braces:

body {color: black}

Note: If the value is multiple words, put quotes around the value:

p {font-family: "sans serif"}

Note: If you wish to specify more than one property, you must separate each property with a semicolon. The example below shows how to define a center aligned paragraph, with a red text color:

p {text-align:center;color:red}

To make the style definitions more readable, you can describe one property on each line, like this:

p

{

text-align: center;

color: black;

font-family: arial

}

Grouping CSS Selectors

You can group selectors. Separate each selector with a comma. In the example below we have grouped all the header elements. All header elements will be displayed in green text color:

h1,h2,h3,h4,h5,h6 

{

color: green

}

The CSS Class Selector

With the class selector you can define different styles for the same type of HTML element.

You might like to have two types of paragraphs in your document: one right-aligned paragraph, and one center-aligned paragraph. Here is how you can do it with styles:

p.right {text-align: right}

p.center {text-align: center}

You have to use the class attribute in your HTML document:

<p class="right">

This paragraph will be right-aligned.

</p>

<p class="center">

This paragraph will be center-aligned.

</p>

Note: Only one class attribute can be specified per HTML element!

You can also omit the tag name in the selector to define a style that will be used by all HTML elements that have a certain class. In the example below, all HTML elements with class="center" will be center-aligned:

.center {text-align: center}

In the code below both the h1 element and the p element have class="center". This means that both elements will follow the rules in the ".center" selector:

<h1 class="center">

This heading will be center-aligned

</h1>

<p class="center">

This paragraph will also be center-aligned.

</p>

Note: Do NOT start a class name with a number! It will not work in Mozilla/Firefox.

The id Selector

You can also define styles for HTML elements with the id selector. The id selector is defined as a #.

The style rule below will match the element that has an id attribute with a value of "green":

#green {color: green}

The style rule below will match the p element that has an id with a value of "parax":

p#parax

{

text-align: center;

color: red

}

Note: Do NOT start an ID name with a number! It will not work in Mozilla/Firefox.

Comments in CSS

Comments are used to explain your code, and may help you when you edit the source code at a later date. A comment will be ignored by browsers. A CSS comment begins with "/*", and ends with "*/", like this:

/* This is a comment */

p

{

text-align: center;

/* This is another comment */

color: black;

font-family: arial

}

How to Insert a Style Sheet

When a browser reads a style sheet, it will format the document according to it. There are three ways of inserting a style sheet:

Recommended! External CSS Style Sheet

An external style sheet is ideal when the style is applied to many pages. With an external style sheet, you can change the look of an entire Web site by changing one file. Each page must link to the style sheet using the <link> tag. The <link> tag goes inside the head section:

<head>

<link rel="stylesheet" type="text/css"

href="mystyle.css" />

</head>

The browser will read the style definitions from the file mystyle.css, and format the document according to it.

An external style sheet can be written in any text editor. The file should not contain any html tags. Your style sheet should be saved with a .css extension. An example of a style sheet file is shown below:

hr {color: black}

p {margin-left: 20px}

body {background-image: url("images/back40.gif")}

Note: Do NOT leave spaces between the property value and the units! If you use "margin-left: 20 px" instead of "margin-left: 20px" it will only work properly in IE6 but it will not work in Mozilla/Firefox or Netscape.

Internal Style Sheet

An internal style sheet should be used when a single document has a unique style. You define internal styles in the head section by using the <style> tag, like this:

<head>

<style type="text/css">

hr {color: black}

p {margin-left: 20px}

body {background-image: url("images/back40.gif")}

</style>

</head>

The browser will now read the style definitions, and format the document according to it.

Note: A browser normally ignores unknown tags. This means that an old browser that does not support styles, will ignore the <style> tag, but the content of the <style> tag will be displayed on the page. It is possible to prevent an old browser from displaying the content by hiding it in the HTML comment element:

<head>

<style type="text/css">

<!--

hr {color: black}

p {margin-left: 20px}

body {background-image: url("images/back40.gif")}

-->

</style>

</head>

Inline Styles

An inline style loses many of the advantages of style sheets by mixing content with presentation. Use this method sparingly, such as when a style is to be applied to a single occurrence of an element.

To use inline styles you use the style attribute in the relevant tag. The style attribute can contain any CSS property. The example shows how to change the color and the left margin of a paragraph:

<p style="color: black; margin-left: 20px">

This is a paragraph

</p>

Multiple Style Sheets

If some properties have been set for the same selector in different style sheets, the values will be inherited from the more specific style sheet. For example, an external style sheet has these properties for the h3 selector:

h3 

{

color: red;

text-align: left;

font-size: 8pt

}

And an internal style sheet has these properties for the h3 selector:

h3 

{

text-align: right; 

font-size: 20pt

}

If the page with the internal style sheet also links to the external style sheet the properties for h3 will be:

color: red; 

text-align: right; 

font-size: 20pt

The color is inherited from the external style sheet and the text-alignment and the font-size is replaced by the internal style sheet.

CSS Background Properties

The CSS background properties allows website designers to control the background color of an element, set an image as the background, repeat a background image vertically or horizontally, and position an image on a page.

Property	Description	Values	IE	F	N	W3C
background	A shorthand property for setting all background properties in one declaration	background-color background-image background-repeat background-attachment background-position	4	1	6	1
background-attachment	Sets whether a background image is fixed or scrolls with the rest of the page	scroll fixed	4	1	6	1
background-color	Sets the background color of an element	color-rgb color-hex color-name transparent	4	1	4	1
background-image	Sets an image as the background	url none	4	1	4	1
background-position	Sets the starting position of a background image	top left top center top right center left center center center right bottom left bottom center bottom right x-% y-% x-pos y-pos	4	1	6	1
background-repeat	Sets if/how a background image will be repeated	repeat repeat-x repeat-y no-repeat	4	1	4	1

CSS Text Properties

The CSS text properties allows website designers to control the appearance of text. It is possible to change the color of a text, increase or decrease the space between characters in a text, align a text, decorate a text, indent the first line in a text, and more.

Property	Description	Values	IE	F	N	W3C
color	Sets the color of a text	color	3	1	4	1
direction	Sets the text direction	ltr rtl	6	1	6	2
letter-spacing	Increase or decrease the space between characters	normal length	4	1	6	1
text-align	Aligns the text in an element	left right center justify	4	1	4	1
text-decoration	Adds decoration to text	none underline overline line-through blink	4	1	4	1
text-indent	Indents the first line of text in an element	length %	4	1	4	1
text-shadow		none color length
text-transform	Controls the letters in an element	none capitalize uppercase lowercase	4	1	4	1
unicode-bidi		normal embed bidi-override	5			2
white-space	Sets how white space inside an element is handled	normal pre nowrap	5	1	4	1
word-spacing	Increase or decrease the space between words	normal length	6	1	6	1

CSS Font Properties

The CSS font properties allows website designers to change the font family, boldness, size, and the style of a text.

Note: In CSS1 fonts are identified by a font name. If a browser does not support the specified font, it will use a default font.

Property	Description	Values	IE	F	N	W3C
font	A shorthand property for setting all of the properties for a font in one declaration	font-style font-variant font-weight font-size/line-height font-family caption icon menu message-box small-caption status-bar	4	1	4	1
font-family	A prioritized list of font family names and/or generic family names for an element	family-name generic-family	3	1	4	1
font-size	Sets the size of a font	xx-small x-small small medium large x-large xx-large smaller larger length %	3	1	4	1
font-size-adjust	Specifies an aspect value for an element that will preserve the x-height of the first-choice font	none number	-	-	-	2
font-stretch	Condenses or expands the current font-family	normal wider narrower ultra-condensed extra-condensed condensed semi-condensed semi-expanded expanded extra-expanded ultra-expanded	-	-	-	2
font-style	Sets the style of the font	normal italic oblique	4	1	4	1
font-variant	Displays text in a small-caps font or a normal font	normal small-caps	4	1	6	1
font-weight	Sets the weight of a font	normal bold bolder lighter 100 200 300 400 500 600 700 800 900	4	1	4	1

CSS Border Properties

The CSS border properties allows website designers to specify the style and color of an element's border. In HTML we use tables to create borders around a text, but with the CSS border properties we can create borders with nice effects, and it can be applied to any element.

Property	Description	Values	IE	F	N	W3C
border	A shorthand property for setting all of the properties for the four borders in one declaration	border-width border-style border-color	4	1	4	1
border-bottom	A shorthand property for setting all of the properties for the bottom border in one declaration	border-bottom-width border-style border-color	4	1	6	1
border-bottom-color	Sets the color of the bottom border	border-color	4	1	6	2
border-bottom-style	Sets the style of the bottom border	border-style	4	1	6	2
border-bottom-width	Sets the width of the bottom border	thin medium thick length	4	1	4	1
border-color	Sets the color of the four borders, can have from one to four colors	color	4	1	6	1
border-left	A shorthand property for setting all of the properties for the left border in one declaration	border-left-width border-style border-color	4	1	6	1
border-left-color	Sets the color of the left border	border-color	4	1	6	2
border-left-style	Sets the style of the left border	border-style	4	1	6	2
border-left-width	Sets the width of the left border	thin medium thick length	4	1	4	1
border-right	A shorthand property for setting all of the properties for the right border in one declaration	border-right-width border-style border-color	4	1	6	1
border-right-color	Sets the color of the right border	border-color	4	1	6	2
border-right-style	Sets the style of the right border	border-style	4	1	6	2
border-right-width	Sets the width of the right border	thin medium thick length	4	1	4	1
border-style	Sets the style of the four borders, can have from one to four styles	none hidden dotted dashed solid double groove ridge inset outset	4	1	6	1
border-top	A shorthand property for setting all of the properties for the top border in one declaration	border-top-width border-style border-color	4	1	6	1
border-top-color	Sets the color of the top border	border-color	4	1	6	2
border-top-style	Sets the style of the top border	border-style	4	1	6	2
border-top-width	Sets the width of the top border	thin medium thick length	4	1	4	1
border-width	A shorthand property for setting the width of the four borders in one declaration, can have from one to four values	thin medium thick length	4	1	4	1

CSS Margin Properties

The CSS margin properties define the space around elements. It is possible to use negative values to overlap content. The top, right, bottom, and left margin can be changed independently using separate properties. A shorthand margin property can also be used to change all of the margins at once.

Note: Netscape and IE give the body tag a default margin of 8px. Opera does not! Instead, Opera applies a default padding of 8px, so if one wants to adjust the margin for an entire page and have it display correctly in Opera, the body padding must be set as well!

Property	Description	Values	IE	F	N	W3C
margin	A shorthand property for setting the margin properties in one declaration	margin-top margin-right margin-bottom margin-left	4	1	4	1
margin-bottom	Sets the bottom margin of an element	auto length %	4	1	4	1
margin-left	Sets the left margin of an element	auto length %	3	1	4	1
margin-right	Sets the right margin of an element	auto length %	3	1	4	1
margin-top	Sets the top margin of an element	auto length %	3	1	4	1

CSS Padding Properties

The CSS padding properties define the space between the element border and the element content. Negative values are not allowed. The top, right, bottom, and left padding can be changed independently using separate properties. A shorthand padding property is also created to control multiple sides at once.

Property	Description	Values	IE	F	N	W3C
padding	A shorthand property for setting all of the padding properties in one declaration	padding-top padding-right padding-bottom padding-left	4	1	4	1
padding-bottom	Sets the bottom padding of an element	length %	4	1	4	1
padding-left	Sets the left padding of an element	length %	4	1	4	1
padding-right	Sets the right padding of an element	length %	4	1	4	1
padding-top	Sets the top padding of an element	length %	4	1	4	1

CSS List Properties

The CSS list properties allows website designers to place the list-item marker, change between different list-item markers, or set an image as the list-item marker.

Property	Description	Values	IE	F	N	W3C
list-style	A shorthand property for setting all of the properties for a list in one declaration	list-style-type list-style-position list-style-image	4	1	6	1
list-style-image	Sets an image as the list-item marker	none url	4	1	6	1
list-style-position	Sets where the list-item marker is placed in the list	inside outside	4	1	6	1
list-style-type	Sets the type of the list-item marker	none disc circle square decimal decimal-leading-zero lower-roman upper-roman lower-alpha upper-alpha lower-greek lower-latin upper-latin hebrew armenian georgian cjk-ideographic hiragana katakana hiragana-iroha katakana-iroha	4	1	4	1
marker-offset		auto length		1	7	2

CSS Dimension Properties

The CSS dimension properties allows website designers to control the height and width of an element. It also allows you to increase the space between two lines.

Property	Description	Values	IE	F	N	W3C
height	Sets the height of an element	auto length %	4	1	6	1
line-height	Sets the distance between lines	normal number length %	4	1	4	1
max-height	Sets the maximum height of an element	none length %	-	1	6	2
max-width	Sets the maximum width of an element	none length %	-	1	6	2
min-height	Sets the minimum height of an element	length %	-	1	6	2
min-width	Sets the minimum width of an element	length %	-	1	6	2
width	Sets the width of an element	auto % length	4	1	4	1

CSS Classification Properties

The CSS classification properties allows website designers to control how to display an element, set where an image will appear in another element, position an element relative to its normal position, position an element using an absolute value, and how to control the visibility of an element.

Property	Description	Values	IE	F	N	W3C
clear	Sets the sides of an element where other floating elements are not allowed	left right both none	4	1	4	1
cursor	Specifies the type of cursor to be displayed	url auto crosshair default pointer move e-resize ne-resize nw-resize n-resize se-resize sw-resize s-resize w-resize text wait help	4	1	6	2
display	Sets how/if an element is displayed	none inline block list-item run-in compact marker table inline-table table-row-group table-header-group table-footer-group table-row table-column-group table-column table-cell table-caption	4	1	4	1
float	Sets where an image or a text will appear in another element	left right none	4	1	4	1
position	Places an element in a static, relative, absolute or fixed position	static relative absolute fixed	4	1	4	2
visibility	Sets if an element should be visible or invisible	visible hidden collapse	4	1	6	2

CSS Positioning Properties

The CSS positioning properties allows website designers to specify the left, right, top, and bottom position of an element. It also allows you to set the shape of an element, place an element behind another, and to specify what should happen when an element's content is too big to fit in a specified area.

Property	Description	Values	IE	F	N	W3C
bottom	Sets how far the bottom edge of an element is above/below the bottom edge of the parent element	auto % length	5	1	6	2
clip	Sets the shape of an element. The element is clipped into this shape, and displayed	shape auto	4	1	6	2
left	Sets how far the left edge of an element is to the right/left of the left edge of the parent element	auto % length	4	1	4	2
overflow	Sets what happens if the content of an element overflow its area	visible hidden scroll auto	4	1	6	2
position	Places an element in a static, relative, absolute or fixed position	static relative absolute fixed	4	1	4	2
right	Sets how far the right edge of an element is to the left/right of the right edge of the parent element	auto % length	5	1	6	2
top	Sets how far the top edge of an element is above/below the top edge of the parent element	auto % length	4	1	4	2
vertical-align	Sets the vertical alignment of an element	baseline sub super top text-top middle bottom text-bottom length %	4	1	4	1
z-index	Sets the stack order of an element	auto number	4	1	6	2

Pseudo-Classes Syntax

The syntax of css pseudo-classes:

selector:pseudo-class {property: value}

CSS classes can also be used with pseudo-classes:

selector.class:pseudo-class {property: value}

Anchor Pseudo-classes

A link that is active, visited, unvisited, or when you mouse over a link can all be displayed in different ways in a modern browser:

a:link {color: #FF0000} /* unvisited link */

a:visited {color: #00FF00} /* visited link */

a:hover {color: #FF00FF} /* mouse over link */

a:active {color: #0000FF} /* selected link */

Note: a:hover MUST come after a:link and a:visited in the CSS definition in order to be effective!!
Note: a:active MUST come after a:hover in the CSS definition in order to be effective!!
Note: Pseudo-class names are not case-sensitive.
Pseudo-classes and CSS Classes

Pseudo-classes can be combined with CSS classes:

a.red:visited {color: #FF0000}

<a class="red" href="css_syntax.asp">CSS Syntax</a>

If the link in the example above has been visited, it will be displayed in red.

CSS2 - The :first-child Pseudo-class

The :first-child pseudo-class matches a specified element that is the first child of another element.

In the example below, the selector matches any p element that is the first child of a div element, and indents the first paragraph inside a div element:

div > p:first-child

{

text-indent:25px

}

This selector will match the first paragraph inside the div in the following HTML:

<div>

<p>

First paragraph in div.

This paragraph will be indented.

</p>

<p>

Second paragraph in div.

This paragraph will not be indented.

</p>

</div>

but it will not match the paragraph in this HTML:

<div>

<h1>Header</h1>

<p>

The first paragraph inside the div.

This paragraph will not be indented.

</p>

</div>

In this example, the selector matches any em element that is the first child of a p element, and sets the font-weight to bold for the first em inside a p element:

p:first-child em

{

font-weight:bold

}

For example, the em in the HTML below is the first child of the paragraph:

<p>I am a <em>strong</em> man.</p>

In this example, the selector matches any a element that is the first child of any element, and sets the text-decoration to none:

a:first-child

{

text-decoration:none

}

For example, the first a in the HTML below is the first child of the paragraph and will not be underlined. But the second a in the paragraph is not the first child of the paragraph and will be underlined:

<p>

Visit <a href="http://www.accessibility101.org.uk/">Accessibility101</a>

and learn about Accessible Website Design.

Visit <a href="http://www.accessibility101.org.uk/">Accessibility101</a>

and learn some Web Accessibility Tips.

</p>

CSS2 - The :lang Pseudo-class

The :lang pseudo-class allows you to define special rules for different languages. In the example below, the :lang class defines the type of quotation marks for q elements with a lang attribute with a value of "no":

<html>

<head>

<style type="text/css">

q:lang(no)

{

quotes: "~" "~"

}

</style>

</head>

<body>

<p>Some text <q lang="no">A quote in a paragraph</q>

Some text.</p>

</body>

</html>

CSS Pseudo-classes

Pseudo-class	Purpose	IE	F	N	W3C
:active	Adds special style to an activated element	4	1	8	1
:focus	Adds special style to an element while the element has focus	-	-	-	2
:hover	Adds special style to an element when you mouse over it	4	1	7	1
:link	Adds special style to an unvisited link	3	1	4	1
:visited	Adds special style to a visited link	3	1	4	1
:first-child	Adds special style to an element that is the first child of some other element		1	7	2
:lang	Allows the author to specify a language to use in a specified element		1	8	2

Pseudo-elements

Pseudo-element	Purpose	IE	F	N	W3C
:first-letter	Adds special style to the first letter of a text	5	1	8	1
:first-line	Adds special style to the first line of a text	5	1	8	1
:before	Inserts some content before an element		1.5	8	2
:after	Inserts some content after an element		1.5	8	2

Media Types

Some CSS properties are only designed for a certain media. For example the "voice-family" property is designed for aural user agents. Some other properties can be used for different media types. For example, the "font-size" property can be used for both screen and print media, but perhaps with different values. A document usually needs a larger font-size on a screen than on paper, and sans-serif fonts are easier to read on the screen, while serif fonts are easier to read on paper.

The @media Rule

The @media rule allows different style rules for different media in the same style sheet.

The style in the example below tells the browser to display a 14 pixels helvetica font on the screen. But if the page is printed, it will be in a 10 pixels Times font. Notice that the font-weight is set to bold, both on screen and on paper:

<html>

<head>

<style>

@media screen

{

p.test {font-family:helvetica,sans-serif; font-size:14px}

}

@media print

{

p.test {font-family:times,serif; font-size:10px}

}

@media screen,print

{

p.test {font-weight:bold}

}

</style>

</head>

<body></body>

</html>

Different Media Types

Note: The media type names are not case-sensitive.

Media Type	Description
all	Used for all media type devices
aural	Used for speech and sound synthesizers
braille	Used for braille tactile feedback devices
embossed	Used for paged braille printers
handheld	Used for small or handheld devices
print	Used for printers
projection	Used for projected presentations, like slides
screen	Used for computer screens
tty	Used for media using a fixed-pitch character grid, like teletypes and terminals
tv	Used for television-type devices

UK Government recommendations:

'Use HTML to structure the document, not style it. Use Cascading Style Sheets to format and style basic elements of a website'

Guidelines for UK Government websites
Illustrated handbook for Web management teams

NEXT >< BACK

Free SEO Advice by Email

Top Ten

The most popular pages in the Hobo Accessibility 101 Archive (by visit).

Website Design Services

Hobo primarily operates in the following areas;

Hobo SEO & Website Design Services

Award Winning Web Design
Useable, Accessible W3C Website Design
Joomla CMS Design & Development
Wordpress Blog Design & Development
HTML & CSS Web Design
E-Commerce Shopping Cart CMS
Hosting & Domain Management
Creative On-Page SEO (Optimization)
Website Text & Image Optimization
Internal Navigation Optimization
Relevant & Quality Link-Building Programme
Web Page SEO Consultation
Social Media Promotion & Networking
Corporate SEO & Online Reputation Management

Contact us

Hobo-Web LTD,
The Stables,
24 Patrick Street,
Greenock
PA16 8NB
Scotland
UK

Telephone 0845 094 0839
FAX 0845 868 8946

Skype: Hobo-Shaun
Contact Us Today
Top Tips SEO Blog

Web Design Tips

Accessibility 101 Accessibility Myths