Text has minimum contrast
Description
This rule checks that the highest possible contrast of every text character with its background meets the minimal contrast requirement.
Applicability
This rule applies to any visible character in a text node that is a child in the flat tree of an HTML element , except if the text node has an ancestor in the flat tree for which at least one of the following is true:
-
disabled
ancestor
:
the
ancestor
is
an
inheriting
semantic
group
orwidget
that is disabled ; or -
disabled
label
:
the
ancestor
is
used
in
the
accessible
name
of
an
inheriting
semantic
widget
that is disabled .
Expectation
For each test target, the highest possible contrast between the foreground colors and background colors is at least 3.0:1 for large scale text and 4.5:1 for other texts, except if the test target is part of a text node that is purely decorative or does not express anything in human language .
Assumptions
-
Success criterion 1.4.3: Contrast (Minimum) has exceptions for “incidental” text, which includes inactive user interface components and decorative texts. The rule assumes that text nodes that should be ignored are disabled or hidden from assistive technologies. If this isn’t the case, the text node could fail this rule while the success criterion could still be satisfied.
-
Success criterion 1.4.3: Contrast (Minimum) also has an exception for logos and brand names. Since logos and brand names are usually displayed through images to ensure correct rendering, this rule does not take logos or brand names into consideration. If a logo or brand name is included using text nodes , the text node could fail while the success criterion could still be satisfied.
-
Text that has the same foreground and background color (a contrast ratio of 1:1) is not considered to be “visual presentation of text”, making it inapplicable to the success criterion. Text hidden in this way can still cause accessibility issues under other success criteria, depending on the content.
-
The definition of disabled element assumes that when the
aria-disabled
attribute is specified on an element, this element has also been disabled for users that do not rely on assistive technology . If this is not the case, that definition may produce incorrect results and in consequence this rule might be Inapplicable to some text nodes that still require a good contrast ratio.
Accessibility Support
- Different browsers have different levels of support for CSS. This can cause contrast issues in one browser that do not appear in another. Because of that, this rule can produce different results depending on the browser that is used. For example, a text that is positioned using CSS transform may be on a different background in a browser that does not support CSS transform.
-
Implementation
of
Presentational
Roles
Conflict
Resolution
varies
from
one
browser
or
assistive
technology
to
another.
Depending
on
this,
some
elements
can
have
a
semantic
role
of
none
and fail this rule with some technology but users of other technologies would not experience any accessibility issue.
Background
Passing this rule does not mean that the text has sufficient color contrast. If all background pixels have a low contrast with all foreground pixels, the success criterion is guaranteed to not be satisfied. When some pixels have sufficient contrast, and others do not, legibility should be considered. There is no clear method for determining legibility when some but not all pixels have sufficient contrast, which is why passing this rule does not necessarily mean the corresponding success criterion is met.
When the text color or background color is not specified in the web page, colors from other origins will be used. Testers must ensure colors are not affected by styles from a user origin , such as a custom style sheet. Contrast issues caused by specifying the text color but not the background or vice versa, must be tested separately from this rule.
Bibliography
- Understanding Success Criterion 1.4.3: Contrast (Minimum)
- Understanding Success Criterion 1.4.6: Contrast (Enhanced)
- G18: Ensuring that a contrast ratio of at least 4.5:1 exists between text (and images of text) and background behind the text
- G145: Ensuring that a contrast ratio of at least 3:1 exists between text (and images of text) and background behind the text
- F83: Failure of Success Criterion 1.4.3 and 1.4.6 due to using background images that do not provide sufficient contrast with foreground text (or images of text)
- CSS Scoping Module Level 1 (Editor’s Draft)
Accessibility Requirements Mapping
-
1.4.3 Contrast (Minimum) (Level AA)
- Learn more about 1.4.3 Contrast (Minimum)
- Required for conformance to WCAG 2.0 and later on level AA and higher.
-
Outcome
mapping:
-
Any
failed
outcomes: success criterion is not satisfied -
All
passed
outcomes: success criterion needs further testing -
An
inapplicable
outcome: success criterion needs further testing
-
Any
Secondary Requirements
This rule is related to the following accessibility requirements, but was not designed to test this requirements directly. These secondary requirements can either be stricter than the rule requires, or may be satisfied in ways not tested by the rule:
- 1.4.6 Contrast (Enhanced) (Level AAA) : This success criterion is more strict than this rule. This is because this criterion has a higher minimum contrast. Some of the passed examples do not satisfy this success criterion.
Input Aspects
The following aspects are required in using this rule.
Test Cases
Passed
Passed Example 1
This dark gray text has a contrast ratio of 12.6:1 on the white background.
<p style="color: #333; background: #FFF;">
Some text in a human language
</p>
Passed Example 2
This dark gray text has a contrast ratio between 12.6:1 and 5:1 on the white to blue gradient background.
<p style="color: #333; background: linear-gradient(to right, #FFF, #00F); width: 500px;">
Some text in a human language
</p>
Passed Example 3
This light gray text has a contrast ratio between 13:1 and 5:1 on the background image.
<style>
p {
color: #ccc;
height: 50px;
padding-top: 15px;
background: #000 no-repeat -20px -20px url('/test-assets/contrast/black-hole.jpeg');
text-shadow: 0px 0px 2px black;
}
</style>
<p>Black hole sun</p>
Passed Example 4
This black text has a contrast ratio between 6.1:1 and 9:1 on gray background with white text shadow on it.
<p style="color: #000; background: #737373; text-shadow: white 0 0 3px">
Some text in a human language
</p>
Passed Example 5
This 18pt large black text has a contrast ratio of 3.6:1 on the gray background.
<p style="color: #000; font-size:18pt; background: #666;">
Some text in a human language
</p>
Passed Example 6
This 14pt bold black text has a contrast ratio of 3.6:1 on the gray background.
<p style="color: #000; font-size:14pt; font-weight:700; background: #666;">
Some text in English
</p>
Passed Example 7
This
text
does
not
convey
anything
in
human
language.
<button style="color: #666; background-color: #000" aria-label="Close">X</button>
Passed Example 8
This text has the default browser text color on the default browser background color. By default this is black text on a white background, which has a contrast ratio of 21:1.
<p>Some text in a human language</p>
Passed Example 9
This dark gray text has a contrast ratio of 12.6:1 on the white background in a shadow DOM tree.
<p style="color: #CCC; background: #fff;" id="p"></p>
<script>
const shadowRoot = document.getElementById('p').attachShadow({ mode: 'open' })
shadowRoot.innerHTML = '<span style="color: #333;">Some text in English</span>'
</script>
Passed Example 10
This
text
has
the
default
user
agent
link
text
and
background
color
,
of
#0000EE
and
white.
This
results
in
a
contrast
ratio
of
9.39:1.
<a href="https://w3c.org/">W3C</a>
Passed Example 11
This text is using the default user agent text color and background color. By default, this is black text on a white background with a contrast ratio of 21:1
<div role="button">My button!</div>
Failed
Failed Example 1
This light gray text has a contrast ratio of 2.3:1 on the white background.
<p style="color: #AAA; background: white;">
Some text in English
</p>
Failed Example 2
This light gray text has a contrast ratio between 1.2:1 and 2.3:1 on the white to blue gradient background.
<p style="color: #AAA; background: linear-gradient(to right, #FFF, #00F); width: 300px">
Some text in English
</p>
Failed Example 3
This light gray text has a contrast ratio between 2.7:1 and 3:1 on the background image.
<p
style="color: #555; height:50px; padding-top:20px; background: black no-repeat -20px -20px url('/test-assets/contrast/black-hole.jpeg');"
>
Black hole sun
</p>
Failed Example 4
This black text with 30% alpha channel has a contrast ratio of 2.1:1 on the white background.
<p style="color: rgba(0,0,0,.3); background: #FFF">
Some text in English
</p>
Failed Example 5
This black text with 30% opacity has a contrast ratio of 2.1:1 on the white background.
<div style="background: #FFF">
<p style="color: #000; opacity: .3">
Some text in English
</p>
</div>
Failed Example 6
This light gray text has a contrast ratio of 2.3:1 on the white background in a shadow DOM tree.
<p style="color: #aaa; background: #fff;" id="p"></p>
<script>
const shadowRoot = document.getElementById('p').attachShadow({ mode: 'open' })
shadowRoot.textContent = 'Some text in English'
</script>
Failed Example 7
This semi-transparent gray text has a contrast ratio between 2.3:1 and 4.2:1 on the black and white background. The light gray text is compared to the white section of the background and the dark gray text is compared to the black section of the background.
<style>
#backgroundSplit {
color: rgba(90, 90, 90, 0.8);
background-position: top 0 left 0;
background-image: linear-gradient(90deg, transparent, transparent 3.3em, black 3.3em, black 6em);
padding: 0 1em;
}
</style>
<span id="backgroundSplit">
Hello world
</span>
Failed Example 8
The
first
p
element
has
a
contrast
ratio
of
12.6:1.
The
second
p
element,
which
contains
an
example
of
the
Helvetica
font,
has
a
contrast
ratio
of
3.85:1.
Because
this
provides
information,
and
is
not
only
for
aesthetic
purposes,
this
is
not
considered
purely
decorative
.
<p style="color: #333; background: #FFF;">
Helvetica is a widely used sans-serif typeface developed in 1957 by Max Miedinger and Eduard Hoffmann.
</p>
<p style="font-family: helvetica; background: #EEE; color: #777;">
The quick brown fox jumps over the lazy dog.
</p>
Failed Example 9
This
text
in
a
button
element
has
a
contrast
ratio
of
3.85:1.
<button style="color: #777; background: #EEE;">My button!</button>
Failed Example 10
This text in a semantic button has a contrast ratio of 3.85:1.
<div role="button" style="color: #777; background: #EEE;">My button!</div>
Inapplicable
Inapplicable Example 1
This
text
is
not
visible
because
of
display:
none
.
<p style="display: none">Some invisible text in English</p>
Inapplicable Example 2
This text is not visible because it is positioned off screen.
<p style="position:absolute; top: -999em">Some invisible text in English</p>
Inapplicable Example 3
This text is not visible because the foreground color is the same as the background color.
<p style="color: white; background: white;" aria-hidden="true">Hidden text - U U D D L R L R B A S</p>
Inapplicable Example 4
This text is not the child of an HTML element.
<svg>
<text x="0" y="15">I love SVG!</text>
</svg>
Inapplicable Example 5
This text not part of a text node .
<p>
<img src="/test-assets/contrast/example.png" alt="example" />
</p>
Inapplicable Example 6
This
text
is
part
of
a
label
of
a
disabled
widget,
because
it
is
in
a
label
element
that
is
the
label
for
an
input
element
with
type="text"
.
<label style="color:#888; background: white;">
My name
<input type="text" disabled />
</label>
Inapplicable Example 7
This
text
is
part
of
a
label
of
a
disabled
widget,
because
it
is
in
an
element
that
is
referenced
by
aria-labelledby
from
an
element
with
role="textbox"
.
<label id="my_pets_name" style="color:#888; background: white;">
My pet's name
</label>
<div
role="textbox"
aria-labelledby="my_pets_name"
aria-disabled="true"
style="height:20px; width:100px; border:1px solid black;"
>
test
</div>
Inapplicable Example 8
This
text
is
part
of
a
label
of
a
disabled
widget,
because
it
is
in
a
label
element
that
is
the
label
for
an
input
element
in
a
fieldset
element
with
the
disabled
attribute.
<fieldset disabled style="color:#888; background: white;">
<label>
My name
<input />
</label>
</fieldset>
Inapplicable Example 9
This
text
is
part
of
a
label
of
a
disabled
widget,
because
it
is
in
a
label
element
that
is
the
label
for
an
input
element
in
an
element
with
role="group"
with
the
aria-disabled="true"
attribute.
<div role="group" aria-disabled="true" style="color:#888; background: white;">
<label>
My name
<input />
</label>
</div>
Inapplicable Example 10
This
text
is
part
of
a
disabled
widget
because
it
is
a
child
of
a
button
element
with
the
disabled
attribute.
<button style="color: #777; background: #EEE;" disabled>My button!</button>
Inapplicable Example 11
This
text
is
part
of
a
disabled
widget
because
it
is
a
child
of
an
element
with
the
role
attribute
set
to
button
and
with
an
aria-disabled
attribute
set
to
true
.
<div role="button" style="color: #777; background: #EEE;" aria-disabled="true">My button!</div>
Glossary
Accessible Name
The accessible name is the programmatically determined name of a user interface element that is included in the accessibility tree .
The accessible name is calculated using the accessible name and description computation .
For native markup languages, such as HTML and SVG, additional information on how to calculate the accessible name can be found in HTML Accessibility API Mappings 1.0, Accessible Name and Description Computation (working draft) and SVG Accessibility API Mappings, Name and Description (working draft) .
For more details, see examples of accessible name .
Note:
As
per
the
accessible
name
and
description
computation
,
each
element
always
has
an
accessible
name.
When
no
accessible
name
is
provided,
the
element
will
nonetheless
be
assigned
an
empty
(
""
)
one.
Note: As per the accessible name and description computation , accessible names are flat string trimmed of leading and trailing whitespace. Notably, it is not possible for a non-empty accessible name to be composed only of whitespace since these must be trimmed.
Attribute value
The attribute value of a content attribute set on an HTML element is the value that the attribute gets after being parsed and computed according to specifications. It may differ from the value that is actually written in the HTML code due to trimming whitespace or non-digits characters, default values, or case-insensitivity.
Some notable case of attribute value, among others:
-
For
enumerated
attributes
,
the
attribute
value
is
either
the
state
of
the
attribute,
or
the
keyword
that
maps
to
it;
even
for
the
default
states.
Thus
<input type="image" />
has an attribute value of eitherImage Button
(the state) orimage
(the keyword mapping to it), both formulations having the same meaning; similarly, “an input element with atype
attribute value ofText
” can be either<input type="text" />
,<input />
(missing value default), or<input type="invalid" />
(invalid value default). -
For
boolean
attributes
,
the
attribute
value
is
true
when the attribute is present andfalse
otherwise. Thus<button disabled>
,<button disabled="disabled">
and<button disabled="">
all have adisabled
attribute value oftrue
. - For attributes whose value is used in a case-insensitive context, the attribute value is the lowercase version of the value written in the HTML code.
- For attributes that accept numbers , the attribute value is the result of parsing the value written in the HTML code according to the rules for parsing this kind of number.
- For attributes that accept sets of tokens, whether space separated or comma separated , the attribute value is the set of tokens obtained after parsing the set and, depending on the case, converting its items to lowercase (if the set is used in a case-insensitive context).
-
For
aria-*
attributes, the attribute value is computed as indicated in the WAI-ARIA specification and the HTML Accessibility API Mappings .
This list is not exhaustive, and only serves as an illustration for some of the most common cases.
The attribute value of an IDL attribute is the value returned on getting it. Note that when an IDL attribute reflects a content attribute, they have the same attribute value.
Background Colors Of Text
The colors of all pixels, excluding the foreground colors pixels, in the bounding box around a visible character in a text node .
Bounding Box around Text
The smallest rectangle that encloses all the visible pixels of a character (including anti-aliased pixels), plus one pixel on every edge (top, right, bottom, left), aligned on the horizontal and vertical axis.
Disabled Element
An element is disabled when it has been rendered inoperable in one or more of the following ways:
-
The element matches the
:disabled
pseudo-class . For HTML elements this means that the element is actually disabled . -
The element has a shadow-including ancestor whose
aria-disabled
attribute value is “true”.
Explicit Semantic Role
The explicit semantic role of an element is determined by its role attribute (if any).
The role attribute takes a list of tokens. The explicit semantic role is the first valid role in this list. The valid roles are all non-abstract roles from WAI-ARIA Specifications . If the element has no role attribute , or if it has one with no valid role, then this element has no explicit semantic role.
Other roles may be added as they become available. Not all roles will be supported in all assistive technologies. Testers are encouraged to adjust which roles are allowed according to the accessibility support base line . For the purposes of executing test cases in all rules, it should be assumed that all roles are supported by assistive technologies so that none of the roles fail due to lack of accessibility support.
Focusable
An element is focusable if one or both of the following are true:
- the element is part of sequential focus navigation ; or
- the element has a tabindex value that is not null.
Exception : Elements that lose focus during a period of up to 1 second after gaining focus, without the user interacting with the page the element is on, are not considered focusable .
Notes:
- The 1 second time span is an arbitrary limit which is not included in WCAG. Given that scripts can manage the focus state of elements, testing the focusability of an element consistently would be impractical without a time limit.
- The tabindex value of an element is the value of the tabindex attribute parsed using the rules for parsing integers . For the tabindex value to be different from null, it needs to be parsed without errors.
Foreground Colors Of Text
The
colors
of
all
the
pixels
of
a
visible
character
in
a
text
node
that
change
color
when
the
CSS
color
property
is
changed.
This
includes
anti-aliased
pixels.
Note: Anti-aliasing is a technique in which the foreground color and background color are blended to create smooth edges.
Highest Possible Contrast
The highest value of the contrast ratios between two sets of colors (A and B). That is, the highest contrast ratio between either the darkest color in A and the brightest color in B, or the brightest color in A and the darkest color in B.
Implicit Semantic Role
The implicit semantic role of an element is a pre-defined value given by the host language which depends on the element and its ancestors.
Implicit roles for HTML and SVG, are documented in the HTML accessibility API mappings (working draft) and the SVG accessibility API mappings (working draft) .
Included in the accessibility tree
Elements included in the accessibility tree of platform specific accessibility APIs are exposed to assistive technologies. This allows users of assistive technology to access the elements in a way that meets the requirements of the individual user.
The general rules for when elements are included in the accessibility tree are defined in the core accessibility API mappings . For native markup languages, such as HTML and SVG, additional rules for when elements are included in the accessibility tree can be found in the HTML accessibility API mappings (working draft) and the SVG accessibility API mappings (working draft) .
For more details, see examples of included in the accessibility tree .
Programmatically
hidden
elements
are
removed
from
the
accessibility
tree.
However,
some
browsers
will
leave
focusable
elements
with
an
aria-hidden
attribute
set
to
true
in
the
accessibility
tree.
Because
they
are
hidden,
these
elements
are
considered
not
included
in
the
accessibility
tree.
This
may
cause
confusion
for
users
of
assistive
technologies
because
they
may
still
be
able
to
interact
with
these
focusable
elements
using
sequential
keyboard
navigation,
even
though
the
element
should
not
be
included
in
the
accessibility
tree.
Inheriting Semantic Role
An element with an inheriting semantic role of X is any element with a non- abstract semantic role that inherits from X, or is the same as X.
Example
:
An
“inheriting
semantic
link”
is
any
element
that
either
has
the
semantic
role
of
link
or
a
semantic
role
that
inherits
from
the
link
role,
such
as
doc-biblioref
.
Large Scale Text
Text
nodes
with
a
-
computed
font-size
of:at least 18 points , or -
at
least
14
points
and
a
computed
font
weight
CSS propertyof 700 or higher.
Marked as decorative
An element is marked as decorative if one or more of the following conditions is true:
-
it
has
an
explicit
role
of
none
orpresentation
; or -
it
is
an
img
element with analt
attribute whose value is the empty string (alt=""
), and with no explicit role .
Elements are marked as decorative as a way to convey the intention of the author that they are pure decoration . It is different from the element actually being pure decoration as authors may make mistakes. It is different from the element being effectively ignored by assistive technologies as rules such as presentational roles conflict resolution may overwrite this intention.
Elements can also be ignored by assistive technologies if they are programmatically hidden . This is different from marking the element as decorative and does not convey the same intention. Notably, being programmatically hidden may change as users interact with the page (showing and hiding elements) while being marked as decorative should stay the same through all states of the page.
Namespaced Element
An
element
with
a
specific
namespaceURI
value
from
HTML
namespaces
.
For
example
an
“SVG
element”
is
any
element
with
the
“SVG
namespace”,
which
is
http://www.w3.org/2000/svg
.
Namespaced
elements
are
not
limited
to
elements
described
in
a
specification.
They
also
include
custom
elements.
Elements
such
as
a
and
title
have
a
different
namespace
depending
on
where
they
are
used.
For
example
a
title
in
an
HTML
page
usually
has
the
HTML
namespace.
When
used
in
an
svg
element,
a
title
element
has
the
SVG
namespace
instead.
Outcome
An outcome is a conclusion that comes from evaluating an ACT Rule on a test subject or one of its constituent test target . An outcome can be one of the three following types:
- Inapplicable: No part of the test subject matches the applicability
- Passed: A test target meets all expectations
- Failed: A test target does not meet all expectations
Note:
A
rule
has
one
passed
or
failed
outcome
for
every
test
target
.
When
there
are
no
test
targets
the
rule
has
one
inapplicable
outcome.
This
means
that
each
test
subject
will
have
one
or
more
outcomes.
Note:
Implementations
using
the
EARL10-Schema
can
express
the
outcome
with
the
outcome
property
.
In
addition
to
passed
,
failed
and
inapplicable
,
EARL
1.0
also
defined
an
incomplete
outcome.
While
this
cannot
be
the
outcome
of
an
ACT
Rule
when
applied
in
its
entirety,
it
often
happens
that
rules
are
only
partially
evaluated.
For
example,
when
applicability
was
automated,
but
the
expectations
have
to
be
evaluated
manually.
Such
“interim”
results
can
be
expressed
with
the
incomplete
outcome.
Programmatically Hidden
An
HTML
element
is
programmatically
hidden
if
either
it
has
a
computed
CSS
property
visibility
whose
value
is
not
visible
;
or
at
least
one
of
the
following
is
true
for
any
of
its
inclusive
ancestors
in
the
flat
tree
:
-
has
a
computed
CSS
property
display
ofnone
; or -
has
an
aria-hidden
attribute set totrue
Note
:
Contrary
to
the
other
conditions,
the
visibility
CSS
property
may
be
reverted
by
descendants.
Note
:
The
HTML
standard
suggests
setting
the
CSS
display
property
to
none
for
elements
with
the
hidden
attribute.
While
not
required
by
HTML,
all
modern
browsers
follow
this
suggestion.
Because
of
this
the
hidden
attribute
is
not
used
in
this
definition.
In
browsers
that
use
this
suggestion,
overriding
the
CSS
display
property
can
reveal
elements
with
the
hidden
attribute.
Semantic Role
The semantic role of an element is determined by the first of these cases that applies:
- Conflict If the element is marked as decorative , but the element is included in the accessibility tree ; or would be included in the accessibility tree when it is not programmatically hidden , then its semantic role is its implicit role .
- Explicit If the element has an explicit role , then its semantic role is its explicit role .
- Implicit The semantic role of the element is its implicit role .
This
definition
can
be
used
in
expressions
such
as
“semantic
button
”
meaning
any
element
with
a
semantic
role
of
button
.
Visible
Content perceivable through sight.
Content is considered visible if making it fully transparent would result in a difference in the pixels rendered for any part of the document that is currently within the viewport or can be brought into the viewport via scrolling.
For more details, see examples of visible .
WAI-ARIA specifications
The WAI ARIA Specifications group both the WAI ARIA W3C Recommendation and ARIA modules, namely:
- Accessible Rich Internet Applications (WAI-ARIA) 1.2
- WAI-ARIA Graphics Module 1.0
- Digital Publishing WAI-ARIA Module 1.0
Note: depending on the type of content being evaluated, part of the specifications might be irrelevant and should be ignored.
Rule Versions
- Proposed version, 30 August 2023 ( compare )
- Latest version, 30 August 2023
Implementations
This section is not part of the official rule. It is populated dynamically and not accounted for in the change history or the last modified date.