This document describes techniques for authoring accessible Cascading Style Sheets (CSS). This is the first Working Draft associated with the latest Web Content Accessibility Guidelines 2.0 Working Draft.

1 Why CSS?

The term "style sheet" comes from the idea of a document that tells a human typesetter the house policies for how documents of particular types (not particular documents) should appear.

David Woolley - 7 May 2001

1 Author benefits

To take advantage of these features in HTML:

Where style sheets have been optional to display HTML content, they are required to display information from XML applications. As explained in question C.22 of The XML FAQ by Peter Flynn:

In HTML, default styling is built into the browsers because the tagset of HTML is predefined and hardwired into browsers. In XML, where you can define your own tagset, browsers cannot know what names you are going to use and what they will mean, so you need a stylesheet if you want to display the formatted text.

Therefore, the differences between CSS for XML and HTML are:

To apply the same external style sheet to both HTML and XML

@@test and confirm these statements.

For more information about XML and CSS:

For more information about creating accessible XML applications refer to the XML Accessibility Guidelines.

2 User benefits

In CSS2, if a user's style sheet contains "!important", it takes precedence over any rule in an author's style sheet. This is different from CSS1, where the author always has final say over styles. For more information on the !important selector refer to the CSS1 and CSS2 specifications. Also, note that since !important was introduced with CSS1 and is more widely implemented than CSS2, the author might have preference over the user in most of the existing user agents. However, it seems that !important is rarely used in author style sheets and therefore might work as defined in CSS2.

For examples of user's style sheets, refer to Appendix ?? - Example user's style sheets.

For more information on the accessibility of CSS refer to:
Think about what needs to change in size and what doesn't. Raster images, for example, have fixed width and heights. We specify them in the img tag in pixels...Similarly, if I just want to move the text away from the border of the page, setting the padding on the body to 5 px shouldn't be a problem. Text, on the other hand, should always be free to change size (a good reason not to use text in images). But when my text doubles in size, do I need the gutter next to it to double in size as well? Probably not. In fact, doubling the gutter might even decrease the usability of the page.

Charles Munat - 6 May 2001

The following CSS2 properties can be used to style text:

  • Case: 'text-transform' (for uppercase, lowercase, and capitalization).
  • Shadow effects: 'text-shadow'
  • Underlines, overlinks, blinking: 'text-decoration'.

Note. If blinking content (e.g., a headline that appears and disappears at regular intervals) is used, provide a mechanism for stopping the blinking. In CSS, 'text-decoration: blink' will cause content to blink and will allow users to stop the effect by turning off style sheets or overriding the rule in a user style sheet. Do not use the BLINK and MARQUEE elements. These elements are not part of any W3C specification for HTML (i.e., they are non-standard elements).

@@ there are no techniques for this category

CSS2 includes several mechanisms that allow content to be generated from style sheets:

  • the :before and :after pseudo-elements and the 'content' property. When used together, these allow authors to insert markers (e.g., counters and constant strings such as "End Example" in the examples below) before or after and element's content.
  • the 'cue', 'cue-before', and 'cue-after' properties. This properties allow users to play a sound before or after an element's content.
  • List styles, which may be numbers, glyphs, or images (usually associated with the LI element in HTML). CSS2 adds international list styles to the styles defined in CSS1. See the 'list-style-type' and 'content' properties.

Generated content can serve as markers to help users navigate a document and stay oriented when they can't access visual clues such as proportional scrollbars, frames with tables of contents, etc.

 Always specify a fallback generic font. BODY { font-family: "Gill Sans", sans-serif } Use CSS properties to format text (: 'font-family', 'font-size', 'font-size-adjust', 'font-stretch', 'font-style', 'font-variant', and 'font-weight'.) Instead of the following deprecated font elements and attributes in HTML: FONT, BASEFONT, "face", and "size". Instead of using deprecated presentation elements and attributes, use the many CSS properties to control font characteristics. 
<STYLE type="text/css">
				P.important { font-weight: bold }
				P.less-important { font-weight: lighter; font-size: smaller }
				H2.subsection { font-family: Helvetica, sans-serif }
				</STYLE>
 If you must use HTML elements to control font information, use BIG and SMALL, which are not deprecated. Color Contrast Use numbers, not names, for colors. 
H1 {color: #808000}
				H1 {color: rgb(50%,50%,0%)}
 
 H1 {color: red}
 Use these CSS properties to specify colors:
  • 'color', for foreground text color.
  • 'background-color', for background colors.
  • 'border-color', 'outline-color' for border colors.
  • For link colors, refer to the :link, :visited, and :active pseudo-classes.
 Ensure that foreground and background colors contrast well. For more information about colors and contrasts, refer to [LIGHTHOUSE] To test whether color contrast is sufficient to be read by people with color deficiencies or by those with low resolution monitors, print pages on a black and white printer (with backgrounds and colors appearing in grayscale). Also try taking the printout and copying it for two or three generations to see how it degrades. This will show you where you need to add redundant cues (example: hyperlinks are usually underlined on Web pages), or whether the cues are too small or indistinct to hold up well. If specifying a foreground color, always specify a background color as well (and vice versa). For example, when asking for input from users, do not write "Please select an item from those listed in green." Instead, ensure that information is available through other style effects (e.g., a font effect) and through context (e.g,. comprehensive text links). Ensure that information is not conveyed through color alone For instance, in this document, examples are styled by default (through style sheets) as follows:
  • They are surrounded by a border.
  • They use a different background color.
  • They begin with the word "Example" or "Deprecated Example".
  • They also end with the phrase "End example", but that phrase is hidden by default with 'display: none'. For user agents that don't support style sheets or when style sheets are turned off, this text helps delineate the end of an example for readers who may not be able to see the border around the example.
 To test whether your document still works without colors, examine it with a monochrome monitor or browser colors turned off. Also, try setting up a color scheme in your browser that only uses black, white, and the four browser-safe greys and see how your page holds up.

Use "em" or % for properties that need to change:

  • font size,
  • line height,
  • @@create exhaustive list. any exceptions?
 Use em to set font sizes 
H1 { font-size: 2em }
 Rather than 
H1 { font-size: 12pt }
 Use px for properties that do not need to change:
  • height and width of raster images,
  • margins,
  • @@create exhaustive list. any exceptions?
 Use relative length units and percentages (@@needs to be fixed). 
BODY { margin-left: 15%; margin-right: 10%}
 Use absolute length units when the physical characteristics of the output medium are known. 
.businesscard { font-size: 8pt }

Using text instead of images means that the information will be available to a greater number of users (with speech synthesizers, braille displays, graphical displays, etc.). Using style sheets will also allow users to override author styles and change colors or fonts sizes more easily.

If it is necessary to use a raster-based images to create a text effect the image must be accessible (refer to the section on text equivalents ).

 Use style sheets to style text rather than representing text in images. The image shows the word "Example" in large, red characters. The alt attribute denotes this. 
<P>This is an 
				<IMG src="BigRedExample.gif" alt="example"> 
				 of what we mean.
				</P>
 This is how to create the large, red character effect with CSS @@to add This image shows text effects that can not yet be created via CSS @@to be created
  • Indentation: 'text-indent'. Do not use the BLOCKQUOTE or any other structural element to indent text.
  • Letter/word spacing: 'letter-spacing', 'word-spacing'.
  • White space: 'white-space'. This property controls the white space processing of an element's content.
  • Text direction: 'direction', 'unicode-bidi'.
  • The :first-letter and :first-line pseudo-elements allow authors to refer to the first letter or line of a paragraph of text.
 Use CSS2 properties to control the formatting and position of text When letters are separated by whitespace they are read as individual letters. Thus, "

H E L L O

" will be read by a screen reader as the individual letters, 'H', 'E', 'L', 'L', 'O' rather than the word "hello." Create the same visual effect with the 'word-spacing' property applied to "HELLO". Text without spaces will be transformed effectively to speech. @@example showing use of "word-spacing" This example shows how to use style sheets to create a drop-cap effect. 
<HEAD>
				<TITLE>Drop caps</TITLE>
				<STYLE type="text/css">
				      .dropcap { font-size : 120%; font-family : Helvetica } 
				</STYLE>
				</HEAD>
				<BODY>
				<P><SPAN class="dropcap">O</SPAN>nce upon a time...
				</BODY>

Rules and borders may convey the notion of "separation" to visually enabled users but that meaning cannot be inferred out of a visual context.

Use these CSS properties to specify border styles:

  • 'border', 'border-width', 'border-style', 'border-color'.
  • 'border-spacing' and 'border-collapse' for tables.
  • 'outline, 'outline-color', 'outline-style', and 'outline-width' for dynamic outlines.
 Use style sheets to create rules and borders. In this example, the H1 element will have a top border that is 2px thick, red, and separated from the content by 1em. 
   <HEAD>
					   <TITLE>Redline with style sheets</TITLE>
					   <STYLE type="text/css">
					        H1 { padding-top: 1em; border-top: 2px red }
					   </STYLE>
					   </HEAD>
					   <BODY>
					   <H1>Chapter 8 - Auditory and Tactile Displays</H1>
					   </BODY>
 If a rule (e.g., the HR element) is used to indicate structure, be sure to indicate the structure in a non-visual way as well. (e.g., by using structural markup). In this example, the DIV element is used to create a navigation bar, which includes a horizontal separator. 
<DIV class="navigation-bar">
					<HR>
					<A rel="Next" href="next.html">[Next page]</A>
				        <A rel="Previous" href="previous.html">[Prevous page]</A>
					<A rel="First" href="first.html">[First page]</A>
					</DIV>
 Provide a text equivalent for any important image or text generated by style sheets (e.g., via the 'background-image', 'list-style', or 'content' properties). @@isn't this saying the same basic thing as the other rule? thus, putting all of the examples in the other rule. assume we can get rid of this one? Ensure that important content appears in the document object. Text generated by style sheets is not part of the document source and will not be available to assistive technologies that access content through the Document Object Model Level 1 ([[DOM1]). @@remove specific reference to Level 1? The following user style sheet generates the words "End Example" after each example in the document. Examples are contained in div elements marked as class "example." 
 
			DIV.example:after {     
			  content: End Example  
			}
 Users can number paragraphs to help locate current reading position in a document. 
 
				P:before {     
				  content: counter(paragraph) ". " ;
  			          counter-increment: paragraph  
				}
 If lists are marked up correctly, i.e. with UL for unordered lists and OL for ordered lists, CSS can be used to provide contextual clues in lists. This CSS2 style sheet provides compound numbers for nested lists created with either UL or OL elements. Items are numbered as "1", "1.1", "1.1.1", etc. 
<STYLE type="text/css">
				    UL, OL { counter-reset: item }
				    LI { display: block }
				    LI:before { content: counters(item, "."); counter-increment: item }
				</STYLE>

Until either CSS2 is widely supported by user agents or user agents allow users to control rendering of lists through other means, consider providing contextual clues in nested lists. The following CSS1 mechanism shows how to hide the end of a list when style sheets are turned on, and to reveal it when style sheets are turned off, when user style sheets override the hiding mechanism, or when style sheets aren't supported.

Note: This example does not help the case of wrapping list items. With some more effort, the author could put similar markup at the end of each list item.

 
  <STYLE type="text/css">
			      .endoflist { display: none }
			  </STYLE>
			  <UL>
			     <LI>Paper:
				<UL>
				   <LI>Envelopes
				   <LI>Notepaper
				   <LI>Letterhead
				   <LI>Poster paper 
				   <span class="endoflist">(End of Paper)</span>
				</UL>
			     <LI>Pens:
				<UL>
				   <LI>Blue writing pens
				   <LI>whiteboard pens 
				   <span class="endoflist">(End of Pens)</span>
				</UL>
			     <LI>Fasteners:
				<UL>
				   <LI>paper clips
				   <LI>staples
				   <LI>Big lengths of rope. 
				   <span class="endoflist">(End of Fasteners)</span>
				</UL> 
			     <span class="endoflist">(End of Office Supplies)</span>
			  </UL>

Layout, positioning, layering, and alignment should be done through style sheets (notably by using CSS floats and absolute positioning):

  • 'text-indent', 'text-align', 'word-spacing', 'font-stretch'. Each of these properties allows users to control spacing without adding additional spaces. Use 'text-align: center' instead of the deprecated CENTER element.
  • 'margin', 'margin-top', 'margin-right', 'margin-bottom', 'margin-left'. With these properties, authors can create space on four sides of an element's content instead of adding non-breaking spaces (&nbsp;).
  • 'float', 'position', 'top', 'right', 'bottom', 'left'. With these properties, the user can control the visual position of almost any element in a manner independent of where the element appears in the document. Authors should always design documents that make sense without style sheets (i.e., the document should be written in a "logical" order) and then apply style sheets to achieve visual effects. The positioning properties may be used to create margin notes (which may be automatically numbered), side bars, frame-like effects, simple headers and footers, and more.
  • The 'empty-cells' property allows users to leave table cells empty and still give them proper borders on the screen or on paper. A data cell that is meant to be empty should not be filled with white space or a non-breaking space just to achieve a visual effect.
 Use style sheets to create layout, positioning, layering, and alignment. If content developers cannot use style sheets and must use invisible or transparent images (e.g., with IMG) to lay out images on the page, they should use alt="". @@instead put a section in HTML techniques and link to that instead of recreating it? Do not use &nbsp; or the text "spacer" as the text equivalent for images. 
   my poem requires a big space<IMG src="10pttab.gif" alt="&nbsp;&nbsp;&nbsp;">here
					   <IMG src="spacer.gif" alt="spacer">
					   <IMG src="colorfulwheel.gif" alt="The wheel of fortune">
Using the positioning properties of CSS2, content may be displayed at any position on the user's viewport. The order in which items appear on a screen may be different than the order they are found in the source document. @@something about using structural markup and document order Turn off style sheets to determine the reading order.

The following example demonstrates a few principles:

  1. the text appears visually in the browser in a different order than in the markup.
  2. CSS positioning may be used to create tabular effects. A TABLE element could have been used to create the same effect.

Note that a class is defined for each object that is being positioned. The use of "id" could be substituted for "class" in these examples. "Class" was used because in the live example, the objects are replicated and thus not unique.

 
<head><style type="text/css">
				  .menu1 { position: absolute; top: 3em; left: 0em; 
					   margin: 0px; font-family: sans-serif; 
					   font-size: 120%; color: red; background-color: white }  
				  .menu2 { position: absolute; top: 3em; left: 10em; 
					   margin: 0px; font-family: sans-serif; 
					   font-size: 120%; color: red; background-color: white }
				  .item1 { position: absolute; top: 7em; left: 0em; margin: 0px }
				  .item2 { position: absolute; top: 8em; left: 0em; margin: 0px }
				  .item3 { position: absolute; top: 9em; left: 0em; margin: 0px }
				  .item4 { position: absolute; top: 7em; left: 14em; margin: 0px }
				  .item5 { position: absolute; top: 8em; left: 14em; margin: 0px }
				  #box { position: absolute; top: 5em; left: 5em } 
				</style></head>
				<body>
				<div class="box">
				  <span class="menu1">Products</span> 
				  <span class="menu2">Locations</span> 
				  <span class="item1">Telephones</span> 
				  <span class="item2">Computers</span> 
				  <span class="item3">Portable MP3 Players</span> 
				  <span class="item5">Wisconsin</span> 
				  <span class="item4">Idaho</span>
				</div>
				</body>
 When style sheets are applied, the text appears in two columns. Elements of class "menu1" (Products) and "menu2" (Locations) appear as column headings. "Telephones, Computers, and Portable MP3 Players" are listed under Products and "Wisconsin" and "Idaho" are listed under Locations. When style sheets are not applied, all of the text appears in one line of words, "Products Locations Telephones Computers Portable MP3 Players Wisconsin Idaho". They appear in the order in which they are written in the source. Therefore, what appear as column headings when style sheets are applied are the first phrases since they were defined first in the source. The following example shows that the same visual appearance may be created in a browser that support style sheets as well as creating a more meaningful presentation when style sheets are not applied. Structural markup (definition lists) have been applied to the content. Note that the margins have been set to 0 since in HTML browsers, definition lists are displayed with a margin set on the DD element. 
<head><style type="text/css">
				  .menu1 { position: absolute; top: 3em; left: 0em; 
					   margin: 0px; font-family: sans-serif; 
					   font-size: 120%; color: red; background-color: white }  
				  .menu2 { position: absolute; top: 3em; left: 10em; 
					   margin: 0px; font-family: sans-serif; 
					   font-size: 120%; color: red; background-color: white }
				  .item1 { position: absolute; top: 7em; left: 0em; margin: 0px }
				  .item2 { position: absolute; top: 8em; left: 0em; margin: 0px }
				  .item3 { position: absolute; top: 9em; left: 0em; margin: 0px }
				  .item4 { position: absolute; top: 7em; left: 14em; margin: 0px }
				  .item5 { position: absolute; top: 8em; left: 14em; margin: 0px }
				  #box { position: absolute; top: 5em; left: 5em } 
				</style></head>
				<body>
				<div class="box">
				<dl>
				  <dt class="menu1">Products</dt>
				    <dd class="item1">Telephones</dd>
				    <dd class="item2">Computers</dd>
				    <dd class="item3">Portable MP3 Players</dd>
				  <dt class="menu2">Locations</dt>
				   <dd class="item4">Idaho</span>
				   <dd class="item5">Wisconsin</span>
				  </dt>
				</dl>
				</div>
				</body>
 When style sheets are applied, it looks as it did before. However, now when the style sheets are not applied, the text appears in a definition list rather than a string of words. What appear as column headings when style sheets are applied, appear as defined terms when style sheets are not applied.

@@discuss ECMAscript, and style sheets, point to the MWC example or "the company" example. examples w/diff markup languages? e.g. HTML, SVG, MathML? points to make/demonstrate:

  • hide/show content,
  • change presentation (movement and colors)
 Aural Cascading Style Sheets

CSS2's aural properties provide information to non-sighted users and voice-browser users much in the same way fonts provide visual information.

The following properties are part of CSS2's aural cascading style sheets.

  • 'volume' controls the volume of spoken text.
  • 'speak' controls whether content will be spoken and, if so, whether it will be spelled or spoken as words.
  • 'pause', 'pause-before', and 'pause-after' control pauses before and after content is spoken. This allows users to separate content for better comprehension.
  • 'cue', 'cue-before', and 'cue-after' specify a sound to be played before and after content, which can be valuable for orientation (much like a visual icon).
  • 'play-during' controls background sounds while an element is rendered (much like a background image).
  • 'azimuth' and 'elevation' provide dimension to sound, which allows users to distinguish voices, for example.
  • 'speech-rate', 'voice-family', 'pitch', 'pitch-range', 'stress', and 'richness' control the quality of spoken content. By varying these properties for different elements, users can fine-tune how content is presented aurally.
  • 'speak-punctuation' and 'speak-numeral' control how numbers and punctuation are spoken, which has an effect on the quality of the experience of aural browsing.

Furthermore, the 'speak-header' property describes how table header information is to be spoken before a table cell.

 This example shows how various sound qualities (including 'voice-family', which is something like an audio font) can let a user know that spoken content is a heading. 
 
				H1 {     
				  voice-family: paul;     
				  stress: 20;     
				  richness: 90;     
				  cue-before: url("ping.au")     
				}
 Access to alternative representations of content

CSS2 lets users access alternative representations of content that is specified in attribute values when the following are used together:

  • attribute selectors.
  • the attr() function and the 'content' property'
  • the :before and :after pseudo-elements
 The value of the "alt" attribute for the IMG element is rendered after the image (visually, aurally, etc.). Note that the value of the attribute is displayed even though the image may not be (e.g., the user has turned off images through the user interface). 
 IMG:after { 
				    content: attr(alt) 
				 }
 Media types The CSS2 "media types" (used with @media rules) allow authors and users to design style sheets that will cause documents to render more appropriately on certain target devices. These style sheets can tailor content for presentation on braille devices, speech synthesizers, or TTY devices. Using "@media" rules can also reduce download times by allowing user agents to ignore inapplicable rules.