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CSS Scrollbars Module Level 1

Editor’s Draft,

Specification Metadata
This version:
https://drafts.csswg.org/css-scrollbars/
Editors:
Tantek Çelik (Mozilla)
(Microsoft)
Suggest an Edit for this Spec:
https://github.com/w3c/csswg-drafts/blob/master/css-scrollbars-1/Overview.bs
Issue Tracking:
GitHub Issues

Abstract

CSS Scrollbars standardizes the ability to color scrollbars introduced in 2000 by Windows IE 5.5. This is useful when building web applications which use color schemes very different from the appearance of default platform scrollbars.

CSS is a language for describing the rendering of structured documents (such as HTML and XML) on screen, on paper, in speech, etc.

Status of this document

This is a public copy of the editors’ draft. It is provided for discussion only and may change at any moment. Its publication here does not imply endorsement of its contents by W3C. Don’t cite this document other than as work in progress.

GitHub Issues are preferred for discussion of this specification. When filing an issue, please put the text “css-scrollbars” in the title, preferably like this: “[css-scrollbars] …summary of comment…”. All issues and comments are archived, and there is also a historical archive.

This document was produced by the CSS Working Group (part of the Style Activity).

This document was produced by a group operating under the W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

This document is governed by the 1 February 2018 W3C Process Document.

1. Introduction

Note: this specification is maintained in the W3C csswg-drafts GitHub repository as css-scrollbars-1 .

1.1. Scope

This subsection is non-normative.

This module adds color properties for styling the scrollbar (if any) of an element per documented use-cases, and as has been increasingly adopted on the web since Windows IE 5.5 introduced it in 2000. [Note: Add citations of examples from Bugzilla 77790 and webcompat].

Out of scope: pseudo-elements for selecting specific parts of a scrollbar are unnecesssary for the documented use-cases and are thus out of scope for this specification.

1.2. Values

This specification follows the CSS property definition conventions from [CSS2]. Value types not defined in this specification are defined in CSS Values & Units [CSS-VALUES-3]. 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 keywords as their property value. For readability they have not been repeated explicitly.

2. Scrollbar Colors: the scrollbar-face-color and scrollbar-track-color properties

Name: scrollbar-face-color, scrollbar-track-color
Value: auto | <color>
Initial: auto
Applies to: boxes to which overflow applies
Inherited: yes
Percentages: n/a
Computed value: the computed color or the keyword auto
Canonical order: per grammar
Animation type: color

These properties allow the author to set colors for various aspects of an element’s scrollbars.

UAs must apply the scrollbar-* values set on the root element to the viewport.

Note: Unlike overflow (and overflow-*) properties, scrollbar-* values set on the HTML body element are not propagated to the viewport.

auto
default platform rendering for that portion of the scrollbar, in the absence of any other related scrollbar color properties. See details below for which scrollbar color are related to which.
<color>
apply the color to that portion of the scrollbar, and potentially other portions of the scrollbar.

Details:

If scrollbar-track-color computes to auto, and scrollbar-face-color is not auto, it is used to color the scrollbar track.

If an element has both horizontal and vertical scrollbars, and the scrollbar-face-color is not auto, use it for the area in the corner between the two scrollbars.

If the color of any part of the scrollbar is specified, implementations may render a simpler scrollbar than the default platform UI rendering, and color it accordingly.

(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 scrollbar color properties for scrollbar parts that do not exist on the underlying platform.

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.

The following example (derived from https://www.w3.org/Style/Examples/007/scrollbars.en.html) resets scrollbar colors in IE.

html { 
    scrollbar-face-color: ThreeDFace;
    scrollbar-track-color: Scrollbar;
}

3. Scrollbar Thickness: the scrollbar-width property

Name: scrollbar-width
Value: auto | thin | <length>
Initial: auto
Applies to: boxes to which overflow applies
Inherited: no
Percentages: n/a
Computed value: absolute length or the keyword auto.
Canonical order: per grammar
Animation type: length

This property allows the author to set the maximum thickness of an element’s scrollbars when they are shown.

auto
implementations must use the default platform scrollbar width.
thin
implementations must use either a thin scrollbar width variant on platforms that provide that option, or display a scrollbar thinner than the default platform scrollbar width.
<length>
When a user agent displays one or more scrollbars for an element, the thickness of those scrollbars must be no more than the computed scrollbar-width length value. Negative <length> values are not allowed. If scrollbar-width computes to 0, the element’s scrollbars are hidden, however its scrollability is not affected.

Note: There is working group disagreement about whether to allow length values, or only have keywords (auto, thin, none), or drop the scrollbar-width property altogether. (Issue 1958)

UAs must apply the scrollbar-width value set on the root element to the viewport.

Note: Unlike overflow (and overflow-*) properties, 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. Acknowledgments

This appendix is informative.

Thanks to the use-cases, prototyping, implementation, and feedback from Tab Atkins and Xidorn Quan.

Appendix B. Changes

This appendix is informative.

This is the First Public Working Draft, no previous draft to describe changes from.

Appendix C. Considerations for Security and Privacy

This appendix is informative.

Per the Self-Review Questionnaire: Security and Privacy: Questions to Consider

  1. Does this specification deal with personally-identifiable information?

    No.

  2. Does this specification deal with high-value data?

    No.

  3. Does this specification introduce new state for an origin that persists across browsing sessions?

    No.

  4. Does this specification expose persistent, cross-origin state to the web?

    No.

  5. Does this specification expose any other data to an origin that it doesn’t currently have access to?

    No.

  6. Does this specification enable new script execution/loading mechanisms?

    No.

  7. Does this specification allow an origin access to a user’s location?

    No.

  8. Does this specification allow an origin access to sensors on a user’s device?

    No.

  9. Does this specification allow an origin access to aspects of a user’s local computing environment?

    No.

  10. Does this specification allow an origin access to other devices?

    No.

  11. Does this specification allow an origin some measure of control over a user agent’s native UI?

    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.

  12. Does this specification expose temporary identifiers to the web?

    No.

  13. Does this specification distinguish between behavior in first-party and third-party contexts?

    No.

  14. How should this specification work in the context of a user agent’s "incognito" mode?

    No differently.

  15. Does this specification persist data to a user’s local device?

    No.

  16. Does this specification have a "Security Considerations" and "Privacy Considerations" section?

    Yes.

  17. Does this specification allow downgrading default security characteristics?

    No.

Conformance

Document conventions

Conformance 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 classes

Conformance to this specification is defined for three conformance classes:

style sheet
A CSS style sheet.
renderer
A UA that interprets the semantics of a style sheet and renders documents that use them.
authoring tool
A UA that writes a style sheet.

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.

Requirements for Responsible Implementation of CSS

The following sections define several conformance requirements for implementing CSS responsibly, in a way that promotes interoperability in the present and future.

Partial Implementations

So 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 property 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 Features

To avoid clashes with future stable CSS features, the CSSWG recommends following best practices for the implementation of unstable features and proprietary extensions to CSS.

Implementations of CR-level Features

Once a specification reaches the Candidate Recommendation stage, implementers should release an unprefixed implementation of any CR-level feature they can demonstrate to be correctly implemented according to spec, and should avoid exposing a prefixed variant of that feature.

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 http://www.w3.org/Style/CSS/Test/. Questions should be directed to the public-css-testsuite@w3.org mailing list.

Index

Terms defined by this specification

Terms defined by reference

References

Normative References

[CSS-COLOR-3]
Tantek Çelik; Chris Lilley; David Baron. CSS Color Module Level 3. 19 June 2018. REC. URL: https://www.w3.org/TR/css-color-3/
[CSS-OVERFLOW-3]
David Baron; Elika Etemad; Florian Rivoal. CSS Overflow Module Level 3. 31 July 2018. WD. URL: https://www.w3.org/TR/css-overflow-3/
[CSS-VALUES-3]
Tab Atkins Jr.; Elika Etemad. CSS Values and Units Module Level 3. 14 August 2018. CR. URL: https://www.w3.org/TR/css-values-3/
[CSS-VALUES-4]
Tab Atkins Jr.; Elika Etemad. CSS Values and Units Module Level 4. 14 August 2018. WD. URL: https://www.w3.org/TR/css-values-4/
[CSS2]
Bert Bos; et al. Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification. 7 June 2011. REC. URL: https://www.w3.org/TR/CSS2/
[RFC2119]
S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. March 1997. Best Current Practice. URL: https://tools.ietf.org/html/rfc2119

Property Index

Name Value Initial Applies to Inh. %ages Anim­ation type Canonical order Com­puted value
scrollbar-face-color auto | <color> auto boxes to which overflow applies yes n/a color per grammar the computed color or the keyword auto
scrollbar-track-color auto | <color> auto boxes to which overflow applies yes n/a color per grammar the computed color or the keyword auto
scrollbar-width auto | thin | <length> auto boxes to which overflow applies no n/a length per grammar absolute length or the keyword auto.