This CSS module defines properties to influence the visual styling of scrollbars, introducing controls for their color and width.
CSSis a language for describing the rendering of structured documents (such as HTML and XML) on screen, on paper, etc.
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Table of ContentsThis section is non-normative.
This CSS module introduces properties to influence the visual styling of scrollbars, including their color (scrollbar-color) and thickness (scrollbar-width).
1.1. ScopeThe CSS Scrollbars Module is specifically for styling scrollbar controls themselves, e.g. their color & width in Level 1, and not their layout nor whether any content is scrollable. All layout impacts and content scrollability are specified in the CSS Overflow Module.
Based on documented use-cases, there are three main use-cases around scrollbars this module intends to resolve:
The internal structure, layout, and configuration of scrollbars, as well as precise control over their coloring, is out of scope. This is because different platforms have different scrollbar structures and styling conventions, and operating systems continuously evolve their scrollbar designs to provide better user experience. Pseudo-elements for selecting specific parts of a scrollbar, for example, were considered and rejected. While this level of fine control would be tempting for authors, the arrangement of the various parts—or whether they’re even all present—cannot be depended on. Providing too much control would allow authors to get perfect results on some platforms, but at the expense of broken results on others.
Note: Exposing the scrollbar-related ::-webkit- prefixed pseudo-elements to the Web is considered a mistake by both the CSS Working Group and Webkit.
This specification follows the CSS property definition conventions from [CSS2] using the value definition syntax from [CSS-VALUES-3]. Value types not defined in this specification are defined in CSS Values & Units [CSS-VALUES-3]. Combination with other CSS modules may expand the definitions of these value types.
In addition to the property-specific values listed in their definitions, all properties defined in this specification also accept the CSS-wide keywords as their property value. For readability they have not been repeated explicitly.
This property allows the author to set colors of an element’s scrollbars.
UAs must apply the scrollbar-color value set on the root element to the viewport.
Note: Unlike overflow (and overflow-*) properties, scrollbar-color value set on the HTML body element are not propagated to the viewport.
Details:
Track refers to the background of the scrollbar, which is generally fixed regardless of the scrolling position.
Thumb refers to the moving part of the scrollbar, which usually floats on top of the track.
If this property computes to a value other than auto, implementations may render a simpler scrollbar than the default platform UI rendering, and color it accordingly.
Note: Sometimes the UA is unable to customize the colors of native scrollbars, perhaps due to how they’re structured, or to a lack of control given by the native toolkit. The provision above allows the UA to replace them with differently-constructed scrollbars, which it does know how to color.
(Note: add diagram showing the different named pieces - something like http://www.howtocreate.co.uk/tutorials/scrlbar.html)
(Note: add example of an overflow element with colorized scrollbars to match page styling, PNG of the same in a browser that supports it currently)
Implementations may ignore any of the colors if the corresponding part do not exist on the underlying platform.
When using scrollbar-color property with specific color values, authors should ensure the specified colors have enough contrast between them. For keyword values, UAs should ensure the colors they use have enough contrast. See WCAG 2.1 SC 1.4.11 Non-text Contrast [WCAG21]. UAs may ignore these contrast requirements based on explicit user preferences (for example, when users choose a configuration option/setting that always ensures a particular scrollbar color / use of system default scrollbars).
Note: when a user interacts with a scrollbar (e.g. hovering or activating), implementations may alter which scrollbar colors apply to which scrollbar parts.
Note: IE uses named System Colors as defaults for each of the scrollbar color properties. See related Issue 1956.
This property allows the author to specify the desired thickness of an element’s scrollbars.
The primary purpose of this property is not to allow authors to chose a particular scrollbar aesthetic for their pages, but to let them indicate for certain small or cramped elements of their pages that a smaller scrollbar would be desirable.
Scrollbars are a UI mechanism essential to interact with the page. Operating systems tend to want consistency in such controls to improve usability through familiarity, and users with specific preferences or needs can adjust the appearance of various UI components, including scrollbars, through OS or UA settings.
While using this property in support of specific UX goals is appropriate, authors should otherwise refrain from overriding such user preferences.
Note: On most systems, this corresponds to the traditional somewhat wide scrollbar. However, through OS or UA settings, users can have the ability to change what this default corresponds to, possibly making the default scrollbar wider or narrower than is typical.
Note: User agents can use various strategies to ensure the usability of narrow scrollbars. For instance, in the case of overlay scrollbars, they can dynamically enlarge the scrollbar in response to a user attempting to interact with it. User agents on devices with touch screens can also adjust how they interpret finger taps to facilitate interacting with visually small touch targets.
User agents may disregard this value and treat it as auto, for instance when the user has indicated discomfort for thin scrollbars through some UA or OS setting. (User agents are encouraged to provide such a setting.)
Note: Some platforms only have a tiny scrollbar by default which cannot be reasonably made thinner. In such cases, this value will behave as auto.
Using this value can prevent mouse-only users from being able to scroll. Authors should ensure that mouse-only users can still reach hidden content, even if they have no scrollwheel.
Authors that use
noneshould provide an alternative/equivalent visual hint that scrolling is possible and there is more content.
Note: For situations where an element is to be scrolled only by programmatic means, and not by direct user manipulation, authors should use overflow: hidden instead of scrollbar-width: none.
Note: Users who find the
thinstyle of scrollbars unusable can include the following rule in their
user style sheet:
* { scrollbar-width: auto !important; }This will ensure that all scrollbars are sized as per OS and UA settings regardless of author styles.
UAs must apply the scrollbar-width value set on the root element to the viewport.
Note: Unlike the overflow property (and its longhands), a scrollbar-width value set on the HTML body element is not propagated to the viewport.
Note: This specification does not define the exact position or shape of the scrollbar, or any animation thereof, such as fading or sliding in/out of view.
Appendix A. AcknowledgmentsThis appendix is non-normative.
Thanks to the use-cases, prototyping, implementation, and feedback from Tab Atkins and Xidorn Quan. Thanks to accessibility review and contributions (#3315) from Patrick H. Lauke.
Appendix B. ChangesThis appendix is non-normative.
Changes since the 2021-12-02 Working DraftBoilerplate changes for CR
Switched "should" to a "must" with regards to accessibility of narrow scrollbars. (see Issue 6675)
This appendix is non-normative.
Considerations for SecurityNo specific concerns regarding security have been identified for this specification.
Considerations for PrivacyNo specific concerns regarding privacy have been identified for this specification.
Self-review questionairePer the Self-Review Questionnaire: Security and Privacy: Questions to Consider
No.
No.
No.
No.
No.
No.
No.
No.
No.
No.
Yes. The scrollbar-* properties enable the page to change the color and width of the scrollbar of the user agent’s native UI, e.g. scrollbars on the page’s window, on framed content embedded in the page, or on overflowing elements with scrollbars in the page.
No.
No.
No differently.
No.
Yes.
No.
This appendix is non-normative.
As noted
in the definition of the property, authors need to be mindful of the accessibility implications of using
scrollbar-width: thin. Scrollbars are a important piece of the user agent’s interface, and it is not appropriate for a web site author to change their size over aesthetic considerations. The property is available to support cases where the author wants to indicate that in a cramped area of the web page a thin scrollbar would be a more effective use of space. However, ultimately, the user, through their user agent, needs to have the last word on such things.
Using this property in such cases is preferable to authors building a custom thin-looking scrollbar in via script or proprietary extensions, because it does give the user the opportunity to override it.
User style sheets do provide such an override, and additionally, user agents are encouraged to expose a setting letting users express that they do not want thin scrollbars to be used.
The CSS Working Group also acknowledges the needs of some users to have scrollbars that are wider than is typical. Operating systems and user agents can offer a means to let users express that preference, and in such cases, CSS will honor that choice.
Conformance Document conventionsConformance requirements are expressed with a combination of descriptive assertions and RFC 2119 terminology. The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in the normative parts of this document are to be interpreted as described in RFC 2119. However, for readability, these words do not appear in all uppercase letters in this specification.
All of the text of this specification is normative except sections explicitly marked as non-normative, examples, and notes. [RFC2119]
Examples in this specification are introduced with the words “for example” or are set apart from the normative text with class="example", like this:
This is an example of an informative example.
Informative notes begin with the word “Note” and are set apart from the normative text with class="note", like this:
Note, this is an informative note.
Advisements are normative sections styled to evoke special attention and are set apart from other normative text with <strong class="advisement">, like this: UAs MUST provide an accessible alternative.
Conformance to this specification is defined for three conformance classes:
A style sheet is conformant to this specification if all of its statements that use syntax defined in this module are valid according to the generic CSS grammar and the individual grammars of each feature defined in this module.
A renderer is conformant to this specification if, in addition to interpreting the style sheet as defined by the appropriate specifications, it supports all the features defined by this specification by parsing them correctly and rendering the document accordingly. However, the inability of a UA to correctly render a document due to limitations of the device does not make the UA non-conformant. (For example, a UA is not required to render color on a monochrome monitor.)
An authoring tool is conformant to this specification if it writes style sheets that are syntactically correct according to the generic CSS grammar and the individual grammars of each feature in this module, and meet all other conformance requirements of style sheets as described in this module.
Partial implementationsSo that authors can exploit the forward-compatible parsing rules to assign fallback values, CSS renderers must treat as invalid (and ignore as appropriate) any at-rules, properties, property values, keywords, and other syntactic constructs for which they have no usable level of support. In particular, user agents must not selectively ignore unsupported component values and honor supported values in a single multi-value property declaration: if any value is considered invalid (as unsupported values must be), CSS requires that the entire declaration be ignored.
Implementations of Unstable and Proprietary FeaturesTo avoid clashes with future stable CSS features, the CSSWG recommends following best practices for the implementation of unstable features and proprietary extensions to CSS.
Non-experimental implementationsOnce a specification reaches the Candidate Recommendation stage, non-experimental implementations are possible, and implementors should release an unprefixed implementation of any CR-level feature they can demonstrate to be correctly implemented according to spec.
To establish and maintain the interoperability of CSS across implementations, the CSS Working Group requests that non-experimental CSS renderers submit an implementation report (and, if necessary, the testcases used for that implementation report) to the W3C before releasing an unprefixed implementation of any CSS features. Testcases submitted to W3C are subject to review and correction by the CSS Working Group.
Further information on submitting testcases and implementation reports can be found from on the CSS Working Group’s website at https://www.w3.org/Style/CSS/Test/. Questions should be directed to the public-css-testsuite@w3.org mailing list.
CR exit criteriaFor this specification to be advanced to Proposed Recommendation, there must be at least two independent, interoperable implementations of each feature. Each feature may be implemented by a different set of products, there is no requirement that all features be implemented by a single product. For the purposes of this criterion, we define the following terms:
The specification will remain Candidate Recommendation for at least six months.
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