CSS Basic User Interface Module Level 3 (CSS3 UI)

Editor’s Draft,

This version:
http://dev.w3.org/csswg/css-ui/
Latest version:
http://www.w3.org/TR/css3-ui/
Previous Versions:
http://www.w3.org/TR/2012/WD-css3-ui-20120117/
Feedback:
www-style@w3.org with subject line “[css-ui] … message topic …” (archives)
Test Suite:
http://test.csswg.org/suites/css-ui-3_dev/nightly-unstable/
Editors:
Tantek Çelik (Mozilla)
Florian Rivoal (Invited Expert)
Issue Tracking:
https://wiki.csswg.org/spec/css3-ui

Abstract

This specification describes user interface related properties and values that are proposed for CSS level 3 to style HTML and XML (including XHTML). It includes and extends user interface related features from the selectors, properties and values of CSS level 2 revision 1 and Selectors specifications. It uses various selectors, properties and values to style basic user interface elements in a document.

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.

The (archived) public mailing list www-style@w3.org (see instructions) is preferred for discussion of this specification. When sending e-mail, please put the text “css-ui” in the subject, preferably like this: “[css-ui] …summary of comment…

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

This document was produced by a group operating under the 5 February 2004 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 August 2014 W3C Process Document.

The following features are at-risk, and may be dropped during the CR period:

Table of Contents

1. Introduction

This module describes CSS properties which enable authors to style user interface related properties and values.

Section 2.1 of CSS1 [CSS1] and Chapter 18 of CSS2 [CSS2] introduced several user interface related properties and values. User Interface for CSS3 (16 February 2000) introduced several new user interface related features.

This Working Draft incorporates, extends, and supersedes them.

1.1. Purpose

The purpose of this specification is to achieve the following objectives:

2. Module Interactions

This document defines new features not present in earlier specifications. In addition, it replaces and supersedes the following:

3. Box Model addition

3.1. box-sizing property

Name: box-sizing
Value: content-box | padding-box | border-box
Initial: content-box
Applies to: all elements that accept width or height
Inherited: no
Percentages: N/A
Media: visual
Computed value: specified value
Animatable: no
content-box
This is the behavior of width and height as specified by CSS2.1. The specified width and height (and respective min/max properties) apply to the width and height respectively of the content box of the element. The padding and border of the element are laid out and drawn outside the specified width and height.
padding-box
Length and percentages values for width and height (and respective min/max properties) on this element determine the padding box of the element. That is, any padding specified on the element is laid out and drawn inside this specified width and height. The content width and height are calculated by subtracting the padding widths of the respective sides from the specified width and height properties. As the content width and height cannot be negative ([CSS21], section 10.2), this computation is floored at 0. Used values, as exposed for instance through getComputedStyle(), also refer to the padding box.
border-box
Length and percentages values for width and height (and respective min/max properties) on this element determine the border box of the element. That is, any padding or border specified on the element is laid out and drawn inside this specified width and height. The content width and height are calculated by subtracting the border and padding widths of the respective sides from the specified width and height properties. As the content width and height cannot be negative ([CSS21], section 10.2), this computation is floored at 0. Used values, as exposed for instance through getComputedStyle(), also refer to the border box.

Note: This is the behavior of width and height as commonly implemented by legacy HTML user agents for replaced elements and input elements.

Note: In contrast to the length and percentage values, the auto value of the width and height properties (as well as other keyword values introduced by later specifications, unless otherwise specified) is not influenced by the box-sizing property, and always sets the size of the content box.

The following terms, whose definitions vary based on the computed value of box-sizing are introduced:

box-sizing: content-box box-sizing: padding-box box-sizing: border-box
min inner width min-width max(0, min-widthpadding-leftpadding-right) max(0, min-widthpadding-leftpadding-rightborder-left-widthborder-right-width)
max inner width max-width max(0, max-widthpadding-leftpadding-right) max(0, max-widthpadding-leftpadding-rightborder-left-widthborder-right-width)
min inner height min-height max(0, min-heightpadding-toppadding-bottom) max(0, min-heightpadding-toppadding-bottomborder-top-widthborder-bottom-width)
max inner height max-height max(0, max-heightpadding-toppadding-bottom) max(0, max-heightpadding-toppadding-bottomborder-top-widthborder-bottom-width)

The Visual formatting model details of [CSS21] are written assuming box-sizing: content-box. The following disambiguations are made to clarify the behavior for all values of box-sizing:

  1. In 10.3.3, the second width in the following phrase is to be interpreted as content width: If width is not auto and border-left-width + padding-left + width + [...]
  2. In 10.3.7, width is to be interpreted as content width in the following equation: left + margin-left + border-left-width + padding-left + width + [...]
  3. In 10.4, width, height, min-width, max-width, min-height and max-height are respectively to be interpreted as content width, content height, min inner width, max inner width, min inner height and max inner height in the following phrases:
    1. The tentative used width is calculated [...]
    2. If the tentative used width is greater than max-width, the rules above are applied again, but this time using the computed value of max-width as the computed value for width.
    3. If the resulting width is smaller than min-width, the rules above are applied again, but this time using the value of min-width as the computed value for width.
    4. Select from the table the resolved height and width values for the appropriate constraint violation. Take the max-width and max-height as max(min, max) so that min ≤ max holds true. In this table w and h stand for the results of the width and height computations [...]
    5. All instances of these words in the table
    6. Then apply the rules under "Calculating widths and margins" above, as if width were computed as this value.
  4. In 10.6.4, height is to be interpreted as content height in the following equation: top + margin-top + border-top-width + padding-top + height + [...]
  5. In 10.7, width, height, min-height and max-height are respectively to be interpreted as content width, content height, min inner height and max inner height in the following phrases:
    1. The tentative used height is calculated [...]
    2. If this tentative height is greater than max-height, the rules above are applied again, but this time using the value of max-height as the computed value for height.
    3. If the resulting height is smaller than min-height, the rules above are applied again, but this time using the value of min-height as the computed value for height.
    4. [...] use the algorithm under Minimum and maximum widths above to find the used width and height. Then apply the rules under "Computing heights and margins" above, using the resulting width and height as if they were the computed values.

Example(s):

Using box-sizing to evenly share space

This example uses box-sizing to evenly horizontally split two divs with fixed size borders inside a div container, which would otherwise require additional markup.

sample CSS:

div.container {
  width:38em;
  border:1em solid black;
}

div.split {
  box-sizing:border-box;
  width:50%;
  border:1em silver ridge;
  float:left;
}

sample HTML fragment:

<div class="container">
<div class="split">This div occupies the left half.</div>
<div class="split">This div occupies the right half.</div>
</div>

demonstration of sample CSS and HTML:

This div should occupy the left half.
This div should occupy the right half.
The two divs above should appear side by side, each (including borders) 50% of the content width of their container. If instead they are stacked one on top of the other then your browser does not support box-sizing.

Note: The padding-box value is at risk.

4. Outline properties

At times, style sheet authors may want to create outlines around visual objects such as buttons, active form fields, image maps, etc., to make them stand out. Outlines differ from borders in the following ways:

  1. Outlines do not take up space.
  2. Outlines may be non-rectangular.
  3. UAs often render outlines on elements in the :focus state.

The outline properties control the style of these dynamic outlines.

The stacking of the rendering of these outlines is explicitly left up to implementations to provide a better user experience per platform. This supersedes the stacking of outlines as defined in CSS 2.1.

Keyboard users depend on outline on elements in the :focus state for interaction with the page, thus authors must not make the outline invisible on such elements without making sure an alternative highlighting mechanism is provided.

The rendering of applying transforms to outlines is left explicitly undefined in CSS3-UI.

4.1. outline property

Name: outline
Value: [ <outline-color> || <outline-style> || <outline-width> ]
Initial: see individual properties
Applies to: all elements
Inherited: no
Percentages: N/A
Media: visual
Computed value: see individual properties
Animatable: see individual properties

4.2. outline-width property

Name: outline-width
Value: <‘border-width’>
Initial: medium
Applies to: all elements
Inherited: no
Percentages: N/A
Media: visual
Computed value: absolute length; 0 if the outline style is none.
Animatable: as length

4.3. outline-style property

Name: outline-style
Value: auto | <‘border-style’>
Initial: none
Applies to: all elements
Inherited: no
Percentages: N/A
Media: visual
Computed value: specified value
Animatable: no

4.4. outline-color property

Name: outline-color
Value: <color> | invert
Initial: invert
Applies to: all elements
Inherited: no
Percentages: N/A
Media: visual
Computed value: The computed value for invert is invert. For <color> values, the computed value is as defined for the [CSS3COLOR] color property.
Animatable: as color

The outline created with the outline properties is drawn "over" a box, i.e., the outline is always on top, and doesn’t influence the position or size of the box, or of any other boxes. Therefore, displaying or suppressing outlines does not cause reflow.

Outlines may be non-rectangular. For example, if the element is broken across several lines, the outline should be an outline or minimum set of outlines that encloses all the element’s boxes.

Each part of the outline should be fully connected rather than open on some sides (as borders on inline elements are when lines are broken).

The parts of the outline are not required to be rectangular. To the extent that the outline follows the border edge, it should follow the border-radius curve.

The position of the outline may be affected by descendant boxes.

User agents should use an algorithm for determining the outline that encloses a region appropriate for conveying the concept of focus to the user.

Note: This specification does not define the exact position or shape of the outline, but it is typically drawn immediately outside the border box.

The outline-width property accepts the same values as border-width ([CSS3BG], Section 4.3).

The outline-style property accepts the same values as border-style ([CSS3BG], Section 4.2), except that hidden is not a legal outline style. In addition, in CSS3, outline-style accepts the value auto. The auto value permits the user agent to render a custom outline style, typically a style which is either a user interface default for the platform, or perhaps a style that is richer than can be described in detail in CSS, e.g. a rounded edge outline with semi-translucent outer pixels that appears to glow. As such, this specification does not define how the outline-color is incorporated or used (if at all) when rendering auto style outlines. User agents may treat auto as solid.

The outline-color property accepts all colors, as well as the keyword invert. Invert is expected to perform a color inversion on the pixels on the screen. This is a common trick to ensure the focus border is visible, regardless of color background.

Conformant UAs may ignore the invert value on platforms that do not support color inversion of the pixels on the screen.

If the UA does not support the invert value then it must reject that value at parse-time, and the initial value of the outline-color property is the currentColor [CSS3COLOR] keyword.

The outline property is a shorthand property, and sets all three of outline-style, outline-width, and outline-color.

Note: The outline is the same on all sides. In contrast to borders, there are no outline-top or outline-left etc. properties.

This specification does not define how multiple overlapping outlines are drawn, or how outlines are drawn for boxes that are partially obscured behind other elements.

Example(s):

Here’s an example of drawing a thick outline around a BUTTON element:

button { outline: thick solid }

Graphical user interfaces may use outlines around elements to tell the user which element on the page has the focus. These outlines are in addition to any borders, and switching outlines on and off should not cause the document to reflow. The focus is the subject of user interaction in a document (e.g., for entering text, selecting a button, etc.).

Example(s):

For example, to draw a thick black line around an element when it has the focus, and a thick red line when it is active, the following rules can be used:

:focus  { outline: thick solid black }
:active { outline: thick solid red }

Note: Since the outline does not affect formatting (i.e., no space is left for it in the box model), it may well overlap other elements on the page.

4.5. outline-offset property

By default, the outline is drawn starting just outside the border edge. However, it is possible to offset the outline and draw it beyond the border edge.

Name: outline-offset
Value: <length>
Initial: 0
Applies to: all elements
Inherited: no
Percentages: N/A
Media: visual
Computed value: <length> value in absolute units (px or physical).
Animatable: as length

If the computed value of outline-offset is anything other than 0, then the outline is outset from the border edge by that amount.

Example(s):

For example, to leave 2 pixels of space between a focus outline and the element that has the focus or is active, the following rule can be used:

:focus,:active  { outline-offset: 2px }

Negative values must cause the outline to shrink into the border box. Both the height and the width of outside of the shape drawn by the outline must not become smaller than twice the computed value of the outline-width property, to make sure that an outline can be rendered even with large negative values. User Agents must apply this constraint independently in each dimension. If the outline is drawn as multiple disconnected shapes, this constraint applies to each shape separately. Negative value constraints are an at risk feature due to interoperability problems, and thus might be dropped from a must to a should.

5. Resizing & Overflow

CSS2.1 provides a mechanism for controlling the appearance of a scrolling mechanism (e.g. scrollbars) on block container elements. This specification adds to that a mechanism for controlling user resizability of elements as well as the ability to specify text overflow behavior.

5.1. resize property

The resize property allows the author to specify whether or not an element is resizable by the user, and if so, along which axis/axes.

Name: resize
Value: none | both | horizontal | vertical
Initial: none
Applies to: elements with overflow other than visible
Inherited: no
Percentages: N/A
Media: visual
Computed value: specified value.
Animatable: no
none
The UA does not present a resizing mechanism on the element, and the user is given no direct manipulation mechanism to resize the element.
both
The UA presents a bidirectional resizing mechanism to allow the user to adjust both the height and the width of the element.
horizontal
The UA presents a unidirectional horizontal resizing mechanism to allow the user to adjust only the width of the element.
vertical
The UA presents a unidirectional vertical resizing mechanism to allow the user to adjust only the height of the element.

Currently it is possible to control the appearance of the scrolling mechanism (if any) on an element using the overflow property (e.g. overflow: scroll vs. overflow: hidden etc.). The purpose of the resize property is to also allow control over the appearance and function of the resizing mechanism (e.g. a resize box or widget) on the element.

Note: The resizing mechanism is NOT the same as the scrolling mechanism. The scrolling mechanism allows the user to determine which portion of the contents of an element is shown. The resizing mechanism allows the user to determine the size of the element.

The resize property applies to elements whose computed overflow value is something other than visible.

The effect of the resize property on generated content is undefined. Implementations should not apply the resize property to generated content.

Note: the resize property may apply to generated content in the future if there is implementation of Interface CSSPseudoElement.

When an element is resized by the user, the user agent sets the width and height properties to px unit length values of the size indicated by the user, in the element’s style attribute DOM, replacing existing property declaration(s) if any, without !important if any.

If an element is resized in only one dimension, only the corresponding property is set, not both.

The precise direction of resizing (i.e. altering the top left of the element or altering the bottom right) may depend on a number of CSS layout factors including whether the element is absolutely positioned, whether it is positioned using the right and bottom properties, whether the language of the element is right-to-left etc. The UA should consider the direction of resizing (as determined by CSS layout), as well as platform conventions and constraints when deciding how to convey the resizing mechanism to the user.

The user agent must allow the user to resize the element with no other constraints than what is imposed by min-width, max-width, min-height, and max-height. (The "must" is at risk since only Firefox currently supports this, and may be downgraded to a "should").

Note: There may be situations where user attempts to resize an element to appear to be overriden or ignored, e.g. because of !important cascading declarations that supersede that element’s style attribute width and height properties in the DOM.

Changes to the computed value of an element’s resize property do not reset changes to the style attribute made due to user resizing of that element.

Example(s):

For example, to make iframes scrollable and resizable, the following rule can be used:

iframe,object[type^="text/"],
object[type$="+xml"],object[type="application/xml"]
{
  overflow:auto;
  resize:both;
}

5.2. Overflow Ellipsis: the text-overflow property

Name: text-overflow
Value: [ clip | ellipsis | <string> ]{1,2}
Initial: clip
Applies to: block containers
Inherited: no
Percentages: N/A
Media: visual
Computed value: as specified
Animatable: no

This property specifies rendering when inline content overflows its line box edge in the inline progression direction of its block container element ("the block") that has overflow other than visible.

Text can overflow for example when it is prevented from wrapping (e.g. due to white-space: nowrap or a single word is too long to fit). Values have the following meanings:

clip
Clip inline content that overflows its block container element. Characters may be only partially rendered.
ellipsis
Render an ellipsis character (U+2026) to represent clipped inline content. Implementations may substitute a more language/script-appropriate ellipsis character, or three dots "..." if the ellipsis character is unavailable.
<string>
Render the given string to represent clipped inline content. The given string is treated as an independent paragraph for bidi purposes.

Note: The <string> value, and the 2-value syntax "{1,2}" and functionality are all at risk.

The term "character" is used in this property definition for better readability and means "grapheme cluster" [UAX29] for implementation purposes.

If there is one value, it applies only to the end line box edge. If there are two values, the first value applies to the line-left edge, and the second value applies to the line-right edge. The terms end, line-left and line-right are defined in [CSS3-WRITING-MODES].

Note: the use of line-left and line-right rather than start and end when there are two values is intentional, to facilitate the use of directional characters such as arrows.

For the ellipsis and string values, implementations must hide characters and atomic inline-level elements at the applicable edge(s) of the line as necessary to fit the ellipsis/string. Place the ellipsis/string immediately adjacent to the applicable edge(s) of the remaining inline content. The first character or atomic inline-level element on a line must be clipped rather than ellipsed.

ellipsing details

user interaction with ellipsis

Example(s):

text-overflow examples

These examples demonstrate setting the text-overflow of a block container element that has text which overflows its dimensions:

sample CSS for a div:

div {  font-family:Helvetica,sans-serif; line-height:1.1;
  width:3.1em; padding:.2em; border:solid .1em black; margin:1em 0;
}

sample HTML fragments, renderings, and your browser:

HTML sample rendering your browser
<div>
CSS IS AWESOME, YES
</div>
First, a box with text drawing outside of it.
CSS IS AWESOME, YES
<div style="text-overflow:clip; overflow:hidden">
CSS IS AWESOME, YES
</div>
Second, a similar box with the text clipped outside the box.
CSS IS AWESOME, YES
<div style="text-overflow:ellipsis; overflow:hidden">
CSS IS AWESOME, YES
</div>
Third, a similar box with an ellipsis representing the clipped text.
CSS IS AWESOME, YES
<div style="text-overflow:ellipsis; overflow:hidden">
NESTED
 <p>PARAGRAPH</p>
WON’T ELLIPSE.
</div>
Fourth, a box with a nested paragraph demonstrating anonymous block boxes equivalency and non-inheritance into a nested element.
NESTED

PARAGRAPH

WON’T ELLIPSE.

Note: the side of the line that the ellipsis is placed depends on the direction of the block. E.g. an overflow hidden right-to-left (direction: rtl) block clips inline content on the left side, thus would place a text-overflow ellipsis on the left to represent that clipped content.

ellipsis interaction with scrolling interfaces

This section applies to elements with text-overflow other than clip (non-clip text-overflow) and overflow:scroll.

When an element with non-clip text-overflow has overflow of scroll in the inline progression dimension of the text, and the browser provides a mechanism for scrolling (e.g. a scrollbar on the element, or a touch interface to swipe-scroll, etc.), there are additional implementation details that provide a better user experience:

When an element is scrolled (e.g. by the user, DOM manipulation), more of the element’s content is shown. The value of text-overflow should not affect whether more of the element’s content is shown or not. If a non-clip text-overflow is set, then as more content is scrolled into view, implementations should show whatever additional content fits, only truncating content which would otherwise be clipped (or is necessary to make room for the ellipsis/string), until the element is scrolled far enough to display the edge of the content at which point that content should be displayed rather than an ellipsis/string.

Example(s):

This example uses text-overflow on an element with overflow scroll to demonstrate the above described behavior.

sample CSS:

div.crawlbar {
  text-overflow: ellipsis;
  height: 2em;
  overflow: scroll;
  white-space: nowrap;
  width: 15em;
  border:1em solid black;
}

sample HTML fragment:

<div class="crawlbar">
CSS is awesome, especially when you can scroll
to see extra text instead of just
having it overlap other text by default.
</div>

demonstration of sample CSS and HTML:

CSS is awesome, especially when you can scroll to see extra text instead of just having it overlap other text by default.

As some content is scrolled into view, it is likely that other content may scroll out of view on the other side. If that content’s block container element is the same that’s doing the scrolling, and the computed value of text-overflow has two values, with the value applying to the start edge being a non-clip value, then implementations must render an ellipsis/string in place of the clipped content, with the same details as described in the value definition above, except that the ellipsis/string is drawn in the start (rather than end) of the block’s direction (per the direction property).

While the content is being scrolled, implementations may adjust their rendering of ellipses/strings (e.g. align to the box edges rather than line edges).

Example(s):

Same as previous example except with text-overflow: ellipsis ellipsis, demonstrated:

CSS is awesome, especially when you can scroll to see extra text instead of just having it overlap other text by default.

If there is insufficient space for both start and end ellipses/strings, then only the end ellipsis/string should be rendered.

6. Pointing Devices and Keyboards

6.1. Pointer interaction

6.1.1. cursor property

Name: cursor
Value: [ [<url> [<x> <y>]?,]*
[ auto | default | none |
context-menu | help | pointer | progress | wait |
cell | crosshair | text | vertical-text |
alias | copy | move | no-drop | not-allowed | grab | grabbing |
e-resize | n-resize | ne-resize | nw-resize | s-resize | se-resize | sw-resize | w-resize | ew-resize | ns-resize | nesw-resize | nwse-resize | col-resize | row-resize | all-scroll | zoom-in | zoom-out
] ]
Initial: auto
Applies to: all elements
Inherited: yes
Percentages: N/A
Media: visual, interactive
Computed value: as specified, except with any relative URLs converted to absolute
Animatable: no
This property specifies the type of cursor to be displayed for the pointing device when within the element’s border-box.

User agents may ignore the cursor property over native user-agent controls such as scrollbars, resizers, or other native UI widgets e.g. those that may be used inside some user agent specific implementations of form elements.

Values have the following meanings:

image cursors

<url>
The user agent retrieves the cursor from the resource designated by the URI. If the user agent cannot handle the first cursor of a list of cursors, it must attempt to handle the second, etc. If the user agent cannot handle any user-defined cursor, it must use the cursor keyword at the end of the list. Conforming User Agents may, instead of <url>, support <image> which is a superset.

The UA must support the following image file formats:

In addition, the UA should support the following image file formats:

The UA may also support additional file formats.

Note: At the time of writing this specification (spring 2015), the only file formats supported for cursors in common desktop browsers are the .ico and .cur file formats, as designed by Microsoft. For compatibility with legacy content, UAs are encouraged to support these, even though the lack of an open specification makes it impossible to have a normative requirement about these formats. Some information on these formats can be found on wikipedia.

The default object size for cursor images is a UA-defined size that should be based on the size of a typical cursor on the UA’s operating system.

The concrete object size is determined using the default sizing algorithm. If an operating system is incapable of rendering a cursor above a given size, cursors larger than that size must be shrunk to within the OS-supported size bounds, while maintaining the cursor image’s intrinsic ratio, if any.

The optional <x> and <y> coordinates identify the exact position within the image which is the pointer position (i.e., the hotspot).

<x>
<y>
Each is a <number>. The x-coordinate and y-coordinate of the position in the cursor’s coordinate system (left/top relative) which represents the precise position that is being pointed to.

If the values are unspecified, then the intrinsic hotspot defined inside the image resource itself is used. If both the values are unspecific and the referenced cursor has no defined hotspot, the effect is as if a value of "0 0" were specified.

If the coordinates of the hotspot, as specified either inside the image resource or by <x> and <y> values, fall outside of the cursor image, they must be clamped (independently) to fit.

general purpose cursors

auto
The UA determines the cursor to display based on the current context, specifically: auto behaves as text over text, and default otherwise.
default
The platform-dependent default cursor. Often rendered as an arrow.
none
No cursor is rendered for the element.

links and status cursors

context-menu
A context menu is available for the object under the cursor. Often rendered as an arrow with a small menu-like graphic next to it.
help
Help is available for the object under the cursor. Often rendered as a question mark or a balloon.
pointer
The cursor is a pointer that indicates a link.
progress
A progress indicator. The program is performing some processing, but is different from wait in that the user may still interact with the program. Often rendered as a spinning beach ball, or an arrow with a watch or hourglass.
wait
Indicates that the program is busy and the user should wait. Often rendered as a watch or hourglass.

selection cursors

cell
Indicates that a cell or set of cells may be selected. Often rendered as a thick plus-sign with a dot in the middle.
crosshair
A simple crosshair (e.g., short line segments resembling a "+" sign). Often used to indicate a two dimensional bitmap selection mode.
text
Indicates text that may be selected. Often rendered as a vertical I-beam. User agents may automatically display a horizontal I-beam/cursor (e.g. same as the vertical-text keyword) for vertical text, or for that matter, any angle of I-beam/cursor for text that is rendered at any particular angle.
vertical-text
Indicates vertical-text that may be selected. Often rendered as a horizontal I-beam.

drag and drop cursors

alias
Indicates an alias of/shortcut to something is to be created. Often rendered as an arrow with a small curved arrow next to it.
copy
Indicates something is to be copied. Often rendered as an arrow with a small plus sign next to it.
move
Indicates something is to be moved.
no-drop
Indicates that the dragged item cannot be dropped at the current cursor location. Often rendered as a hand or pointer with a small circle with a line through it.
not-allowed
Indicates that the requested action will not be carried out. Often rendered as a circle with a line through it.
grab
Indicates that something can be grabbed (dragged to be moved). Often rendered as the backside of an open hand.
grabbing
Indicates that something is being grabbed (dragged to be moved). Often rendered as the backside of a hand with fingers closed mostly out of view.

resizing and scrolling cursors

e-resize, n-resize, ne-resize, nw-resize, s-resize, se-resize, sw-resize, w-resize
Indicates that some edge is to be moved. For example, the se-resize cursor is used when the movement starts from the south-east corner of the box.
ew-resize, ns-resize, nesw-resize, nwse-resize
Indicates a bidirectional resize cursor.
col-resize
Indicates that the item/column can be resized horizontally. Often rendered as arrows pointing left and right with a vertical bar separating them.
row-resize
Indicates that the item/row can be resized vertically. Often rendered as arrows pointing up and down with a horizontal bar separating them.
all-scroll
Indicates that the something can be scrolled in any direction. Often rendered as arrows pointing up, down, left, and right with a dot in the middle.

zooming cursors

zoom-in, zoom-out
Indicates that something can be zoomed (magnified) in or out, and often rendered as a magnifying glass with a "+" or "-" in the center of the glass, for zoom-in and zoom-out respectively.

The UA may treat unsupported values as auto. E.g. on platforms that do not have a concept of a context-menu cursor, the UA may render default or whatever is appropriate.

Example: cursor fallback

Here is an example of using several cursor values.

:link,:visited {
    cursor: url(example.svg#linkcursor),
            url(hyper.cur),
            url(hyper.png) 2 3,
            pointer
}

This example sets the cursor on all hyperlinks (whether visited or not) to an external SVG cursor ([SVG10], section 16.8.3). User agents that don’t support SVG cursors would simply skip to the next value and attempt to use the "hyper.cur" cursor. If that cursor format was also not supported, the UA could attempt to use the "hyper.png" cursor with the explicit hot spot. Finally if the UA does not support any of those image cursor formats, the UA would skip to the last value and render the pointer cursor.

6.1.1.1. Cursor of the canvas

The document canvas is the infinite surface over which the document is rendered [CSS21]. Since no element corresponds to the canvas, in order to allow styling of the cursor when not over any element, the canvas cursor re-uses the root element’s cursor. However, if no boxes are generated for the root element (for example, if the root element has display: none), then the canvas cursor is the platform-dependent default cursor.

Note: An element might be invisible, but still generate boxes. For example, if the element has visibility: hidden but not display: none, boxes are generated for it and its cursor is used for the canvas.

6.2. Insertion caret

6.2.1. Coloring the insertion caret: caret-color

Name: caret-color
Value: auto | <color>
Initial: auto
Applies to: elements that accept input
Inherited: yes
Percentages: N/A
Media: interactive
Computed value: The computed value for auto is auto. For <color> values, the computed value is as defined for the [CSS3COLOR] color property.
Animatable: no
auto
User agents should use currentColor. User agents may automatically adjust the color of caret to ensure good visibility and contrast with the surrounding content, possibly based on the currentColor, background, shadows, etc.
<color>
the insertion caret is colored with the specified color.

The caret is a visible indicator of the insertion point in an element where text (and potentially other content) is inserted by the user. This property controls the color of that visible indicator.

Note: caret shape and blinking is outside the scope of this feature and thus unspecified.

Example: a textarea with caret-color:#00aacc;

Note: The caret-color property is at risk.

6.3. Keyboard control

Name: nav-up, nav-right, nav-down, nav-left
Value: auto | <id> [ current | root | <target-name> ]?
Initial: auto
Applies to: all enabled elements
Inherited: no
Percentages: N/A
Media: interactive
Computed value: as specified
Animatable: no
auto
The user agent automatically determines which element to navigate the focus to in response to directional navigational input.
<id>

The <id> value is an ID selector [SELECT]. In response to directional navigation input corresponding to the property, the focus is navigated to the first element in tree order matching the selector.

If this refers to the currently focused element, the directional navigation input respective to the nav- property is ignored — there is no need to refocus the same element.

If no element matches the selector, the user agent automatically determines which element to navigate the focus to.

If the focus is navigated to an element that was not otherwise focusable, it becomes focusable only as the result of this directional navigation, and the :focus pseudo-class matches the element while it is focused as such.

Note: there were other options under consideration for such "not otherwise focusable" elements, including focus to the next otherwise focusable element in the document tree (including descendants of such a not otherwise focusable element). Input on such other options is welcome and explicitly solicited, especially from implementation experiences and author experience using the directional navigation properties in their content.

<target-name>
The <target-name> parameter indicates the target frame for the focus navigation. It is a <string> and it MUST NOT start with the underscore "_" character. Error handling: if it does start with an underscore, "_parent" navigates to the parent frame, "_root" is treated as root, and other values navigate to a frame by that name if it exists. If the specified target frame does not exist, the parameter will be treated as the keyword current, which means to simply use the frame that the element is in. The keyword root indicates that the user agent should target the full window.

User agents for devices with directional navigation keys respond by navigating the focus according to four respective nav-* directional navigation properties (nav-up, nav-right, nav-down, nav-left). This specification does not define which keys of a device are directional navigational keys.

Note: Typical personal computers have keyboards with four arrow keys. One possible implementation would be to use those four arrow keys for directional navigation. For accessibility and user convenience, user agents should allow configuration of which keys on a keyboard are used for directional navigation.

6.3.1.1. Example: positioned buttons

Here is an example of buttons positioned in a diamond shape whose directional focus navigation is set in such a way to navigate the focus clockwise (or counter-clockwise) around the diamond shape when the user chooses to navigate directionally.

button { position:absolute }

button#b1 {
  top:0; left:50%;
  nav-right:#b2; nav-left:#b4;
  nav-down:#b2; nav-up:#b4;
}

button#b2 {
  top:50%; left:100%;
  nav-right:#b3; nav-left:#b1;
  nav-down:#b3; nav-up:#b1;
}

button#b3 {
  top:100%; left:50%;
  nav-right:#b4; nav-left:#b2;
  nav-down:#b4; nav-up:#b2;
}

button#b4 {
  top:50%; left:0;
  nav-right:#b1; nav-left:#b3;
  nav-down:#b1; nav-up:#b3;
}

Whatever markup sequence the buttons may have (which is not specified in this example) is irrelevant in this case because they are positioned, and yet, it is still important to ensure focus navigation behaviors which relate reasonably to the specified layout.

6.3.1.2. Example: moving focus to inside a frame

Moving the focus to an element in a specific frame requires both the element’s id and the frame’s name.

This example shows how to make navigating left from the button with id "foo" move the focus to the element with id "bar" within the frame named "sidebar".

button#foo { nav-left: #bar "sidebar"; }

6.3.2. Obsolete: the ime-mode property

"ime-mode" is a property somewhat implemented in some browsers, that is problematic and officially obsoleted by this specification.

There is documentation of non-interoperability of these implementations.

User agents should not support the ime-mode property.

Authors must not use the ime-mode property.

Users may use the ime-mode property only for repair use-cases where they have to work around bad sites and legacy implementations, e.g. with a user style sheet rule like:

Example: user preference

input[type=password] {    ime-mode: auto !important;
}

This example CSS may be placed into a user style sheet file to force password input fields to behave in a default manner.

This specification deliberately does not attempt to document the functionality of legacy ime-mode implementations nor what they specifically support because it does not make sense to pursue or recommend any such path.

Note: there are several [HTML5] features which authors should use to provide information to user agents that allow them to provide a better input user experience:

Appendix A. Acknowledgments

This appendix is informative.

This specification was edited and written for the most part by Tantek Çelik from 1999 to the present, first while representing Microsoft, then as an invited expert, and most recently while representing Mozilla.

Thanks to Florian Rivoal for his recent work documenting issues from www-style emails, proposing resolutions & changes, and in particular for researching & writing greatly improved details for the box-sizing property.

Thanks to feedback and contributions from Rossen Atanassov, Tab Atkins, L. David Baron, Bert Bos, Matthew Brealey, Rick Byers, Ada Chan, James Craig, Michael Cooper, Axel Dahmen, Michael Day, Micah Dubinko, Elika E., Steve Falkenburg, Andrew Fedoniouk, Al Gilman, Ian Hickson, Bjoern Hoehrmann, Alan Hogan, David Hyatt, Richard Ishida, Sho Kuwamoto, Yves Lafon, Stuart Langridge, Susan Lesch, Peter Linss, Kang-Hao Lu, Masayuki Nakano, Mats Palmgren, Brad Pettit, François Remy, Andrey Rybka, Simon Sapin, Alexander Savenkov, Sebastian Schnitzenbaumer, Lea Verou, Etan Wexler, David Woolley, Frank Yan, Boris Zbarsky, and Domel.

Appendix B. Changes

This appendix is informative.

In general this draft contains editorial/grammatical/spelling corrections, and a few new informative examples. This appendix describes functional changes from the Working Draft (WD) of 17 Jan 2012 that were made to reflect implementer adoption (or lack thereof), as well as implementer innovations. In particular, changes since the previous draft fall into one of three categories:

List of substantial changes

Appendix C. Default style sheet additions for HTML

This appendix is informative.

Potential additions to the base style sheet to express HTML form controls, and a few dynamic presentation attributes:

:enabled:focus {
 outline: 2px inset;
}

button,
input[type=button],
input[type=reset],
input[type=submit],
input[type=checkbox],
input[type=radio],
textarea,
input,
input[type=text],
input[type=hidden],
input[type=password],
input[type=image]
{
 display: inline-block;
 white-space: nowrap;
}

button
{
/* white space handling of BUTTON tags in particular */
 white-space:normal;
}

input[type=reset]:lang(en)
{
/* default content of HTML input type=reset button, per language */
 content: "Reset";
}

input[type=submit]:lang(en)
{
/* default content of HTML input type=submit button, per language */
 content: "Submit";
}

/* UAs should use language-specific Reset/Submit rules for others. */

input[type=button],
input[type=reset][value],
input[type=submit][value]
{
/* text content/labels of HTML "input" buttons */
 content: attr(value);
}

textarea
{
/* white space handling of TEXTAREA tags in particular */
 white-space:pre-wrap;
}

input[type=hidden]
{
/* appearance of the HTML hidden text field in particular */
 display: none;
}

input[type=image]
{
 display: inline-block;
 content: attr(src,url);
 border: none;
}

select[size]
{
/* HTML4/XHTML1 <select> w/ size more than 1 - appearance of list */
 display: inline-block;
 height: attr(size,em);
}

select,select[size=1]
{
/* HTML4/XHTML1 <select> without size, or size=1 - popup-menu */
 display: inline-block;
 height: 1em;
 overflow: hidden;
}

select[size]:active
{
/* active HTML <select> w/ size more than 1 - appearance of active list */
 display: inline-block;
}

optgroup,option
{
 display: block;
 white-space: nowrap;
}

optgroup[label],option[label]
{
 content: attr(label);
}

option[selected]::before
{
 display: inline;
 content: check;
}

/* Though FRAME resizing is not directly addressed by this specification,
   the following rules may provide an approximation of reasonable behavior. */

/*

frame { resize:both }
frame[noresize] { resize:none }

*/

Appendix D: Test Suite

This appendix is informative.

There is a partial test suite written according to the CSS Test Suite Documentation and following the CSS2.1 Test Case Authoring Guidelines. The test suite shall allow user agents to verify their basic conformance to the specification. This test suite does not pretend to be exhaustive and does not cover all possible combinations of user interface related features. These tests will be made available from the CSS Test Suites home page.

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.

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 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.

Experimental implementations

To avoid clashes with future CSS features, the CSS2.1 specification reserves a prefixed syntax for proprietary and experimental extensions to CSS.

Prior to a specification reaching the Candidate Recommendation stage in the W3C process, all implementations of a CSS feature are considered experimental. The CSS Working Group recommends that implementations use a vendor-prefixed syntax for such features, including those in W3C Working Drafts. This avoids incompatibilities with future changes in the draft.

Non-experimental implementations

Once 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 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

[CSS21]
Bert Bos; et al. Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification. 7 June 2011. W3C Recommendation. URL: http://www.w3.org/TR/2011/REC-CSS2-20110607
[CSS3-WRITING-MODES]
Elika J. Etemad; Koji Ishii. CSS Writing Modes Module Level 3. 15 November 2012. W3C Working Draft. (Work in progress.) URL: http://www.w3.org/TR/2012/WD-css3-writing-modes-20121115/
[CSS3BG]
Bert Bos; Elika J. Etemad; Brad Kemper. CSS Backgrounds and Borders Module Level 3. 24 July 2012. W3C Candidate Recommendation. (Work in progress.) URL: http://www.w3.org/TR/2012/CR-css3-background-20120724/
[CSS3COLOR]
Tantek Çelik; Chris Lilley; L. David Baron. CSS Color Module Level 3. 7 June 2011. W3C Recommendation. URL: http://www.w3.org/TR/2011/REC-css3-color-20110607
[PNG]
Tom Lane. Portable Network Graphics (PNG) Specification (Second Edition). 10 November 2003. REC. URL: http://www.w3.org/TR/PNG
[SVG]
Jon Ferraiolo. Scalable Vector Graphics (SVG) 1.0 Specification. 4 September 2001. REC. URL: http://www.w3.org/TR/SVG/
[UAX29]
Mark Davis. Text Boundaries. 25 March 2005. Unicode Standard Annex #29. URL: http://www.unicode.org/unicode/reports/tr29/tr29-9.html
[CSS-BACKGROUNDS-3]
CSS Backgrounds and Borders Module Level 3 URL: http://www.w3.org/TR/css3-background/
[CSS-CASCADE-4]
CSS Cascading and Inheritance Level 4 URL: http://dev.w3.org/csswg/css-cascade-4/
[CSS-COLOR-3]
CSS Color Module Level 3 URL: http://www.w3.org/TR/css3-color/
[CSS-IMAGES-3]
CSS Image Values and Replaced Content Module Level 3 URL: http://www.w3.org/TR/css3-images/
[CSS-OVERFLOW-3]
David Baron. CSS Overflow Module Level 3. 18 April 2013. WD. URL: http://www.w3.org/TR/css-overflow-3/
[CSS-POSITION-3]
CSS Positioned Layout Module Level 3 URL: http://www.w3.org/TR/css3-positioning/
[CSS-VALUES-3]
CSS Values and Units Module Level 3 URL: http://www.w3.org/TR/css3-values/
[CSS-WRITING-MODES-3]
Elika Etemad; Koji Ishii. CSS Writing Modes Level 3. 20 March 2014. CR. URL: http://www.w3.org/TR/css-writing-modes-3/
[CSSOM-1]
CSS Object Model Level 1 URL: http://www.w3.org/TR/cssom/
[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
[SVG-INTEGRATION]
Cameron McCormack; Doug Schepers; Dirk Schulze. SVG Integration. 17 April 2014. WD. URL: http://www.w3.org/TR/svg-integration/

Informative References

[CSS1]
Håkon Wium Lie; Bert Bos. Cascading Style Sheets (CSS1) Level 1 Specification. 11 April 2008. REC. URL: http://www.w3.org/TR/CSS1/
[CSS2]
Bert Bos; et al. Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification. 7 June 2011. REC. URL: http://www.w3.org/TR/CSS2
[CSSUI]
Tantek Çelik. User Interface for CSS3. 16 February 2000. W3C Working Draft. (Superseded) URL: http://www.w3.org/TR/2002/WD-css3-userint-20020802
[SELECT]
Tantek Çelik; et al. Selectors Level 3. 29 September 2011. W3C Recommendation. URL: http://www.w3.org/TR/2011/REC-css3-selectors-20110929/
[SVG10]
Jon Ferraiolo. Scalable Vector Graphics (SVG) 1.0 Specification. 4 September 2001. W3C Recommendation. URL: http://www.w3.org/TR/2001/REC-SVG-20010904
[HTML5]
Ian Hickson; et al. HTML5. 28 October 2014. REC. URL: http://www.w3.org/TR/html5/

Property Index

Name Value Initial Applies to Inh. %ages Media Animatable Computed value
box-sizing content-box | padding-box | border-box content-box all elements that accept width or height no N/A visual no specified value
outline [ <outline-color> || <outline-style> || <outline-width> ] see individual properties all elements no N/A visual see individual properties see individual properties
outline-width <‘border-width’> medium all elements no N/A visual as length absolute length; 0 if the outline style is none.
outline-style auto | <‘border-style’> none all elements no N/A visual no specified value
outline-color <color> | invert invert all elements no N/A visual as color The computed value for invert is invert. For <color> values, the computed value is as defined for the [CSS3COLOR] color property.
outline-offset <length> 0 all elements no N/A visual as length <length> value in absolute units (px or physical).
resize none | both | horizontal | vertical none elements with overflow other than visible no N/A visual no specified value.
text-overflow [ clip | ellipsis | <string> ]{1,2} clip block containers no N/A visual no as specified
cursor [ [<url> [<x> <y>]?,]* [ auto | default | none | context-menu | help | pointer | progress | wait | cell | crosshair | text | vertical-text | alias | copy | move | no-drop | not-allowed | grab | grabbing | e-resize | n-resize | ne-resize | nw-resize | s-resize | se-resize | sw-resize | w-resize | ew-resize | ns-resize | nesw-resize | nwse-resize | col-resize | row-resize | all-scroll | zoom-in | zoom-out ] ] auto all elements yes N/A visual, interactive no as specified, except with any relative URLs converted to absolute
caret-color auto | <color> auto elements that accept input yes N/A interactive no The computed value for auto is auto. For <color> values, the computed value is as defined for the [CSS3COLOR] color property.
nav-up auto | <id> [ current | root | <target-name> ]? auto all enabled elements no N/A interactive no as specified
nav-right auto | <id> [ current | root | <target-name> ]? auto all enabled elements no N/A interactive no as specified
nav-down auto | <id> [ current | root | <target-name> ]? auto all enabled elements no N/A interactive no as specified
nav-left auto | <id> [ current | root | <target-name> ]? auto all enabled elements no N/A interactive no as specified