Editor’s Draft, 2 April 2026
More details about this documentCopyright © 2026 World Wide Web Consortium. W3C® liability, trademark and permissive document license rules apply.
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 properties and values of CSS level 2 revision 1. It uses various 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, etc.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.
Please send feedback by filing issues in GitHub (preferred), including the spec code “css-ui” in the title, like this: “[css-ui] …summary of comment…”. All issues and comments are archived. Alternately, feedback can be sent to the (archived) public mailing list www-style@w3.org.
This document is governed by the 18 August 2025 W3C Process Document.
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 specification incorporates, extends, and supersedes them.
TestsBasic UI tests
The purpose of this specification is to achieve the following objectives:
This document defines new features not present in earlier specifications. In addition, it replaces and supersedes the following:
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.
| box-sizing |
| content-box | border-box |
| content-box |
| all elements that accept width or height |
| no |
| N/A |
| specified value |
| per grammar |
| discrete |
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:
| min-width | max(0, min-width − padding-left − padding-right − border-left-width − border-right-width) |
| max-width | max(0, max-width − padding-left − padding-right − border-left-width − border-right-width) |
| min-height | max(0, min-height − padding-top − padding-bottom − border-top-width − border-bottom-width) |
| max-height | max(0, max-height − padding-top − padding-bottom − border-top-width − border-bottom-width) |
The Visual formatting model details of [CSS2] are written assuming box-sizing: content-box. The following disambiguations are made to clarify the behavior for all values of box-sizing:
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:
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:
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 Appendix E of CSS 2.1 [CSS2].
Keyboard users, in particular people with disabilities who may not be able to interact with the page in any other fashion, depend on the outline being visible on elements in the :focus state, 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.
Tests| outline |
| [ <'outline-color'> || <'outline-style'> || <'outline-width'> ] |
| see individual properties |
| all elements |
| no |
| N/A |
| see individual properties |
| see individual properties |
| per grammar |
| outline-width |
| <line-width> |
| medium |
| all elements |
| no |
| N/A |
| absolute length , snapped as a border width ; 0 if the outline style is none. |
| per grammar |
| length by computed value |
| outline-style |
| auto | <border-style> |
| none |
| all elements |
| no |
| N/A |
| as specified |
| per grammar |
| discrete |
| outline-color |
| <color> | invert |
| invert |
| all elements |
| no |
| N/A |
| The computed value for invert is invert; the computed value of currentColor is currentColor (See currentcolor); see the color property for other <color> values. |
| per grammar |
| color by computed value |
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 (CSS Backgrounds 3 § 3.3 Line Thickness: the border-width properties).
The outline-style property accepts the same values as border-style (CSS Backgrounds 3 § 3.2 Line Patterns: the border-style properties), 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 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.
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 or selecting a button).
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.
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.
| outline-offset |
| <length> |
| 0 |
| all elements |
| no |
| N/A |
| <length> value in absolute units (px or physical). absolute length |
| per grammar |
| length by computed value |
If the computed value of outline-offset is anything other than 0, then the outline is outset from the border edge by that amount.
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 should 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 should apply this constraint independently in each dimension. If the outline is drawn as multiple disconnected shapes, this constraint applies to each shape separately.
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.
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.
| resize |
| none | both | horizontal | vertical |
| none |
| elements with overflow other than visible, that are scroll containers and optionally replaced elements such as images, videos, and iframes |
| no |
| N/A |
| as specified keyword |
| per grammar |
| discrete |
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 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, nor is it related to any UA mechanism for zooming. 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. that are scroll containers. UAs may also apply it, regardless of the value of the overflow property, to:
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 the CSSPseudoElement interface (See [css-pseudo-4]).
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.
Note: There may be situations where user attempts to resize an element appear to be overridden 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.
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; }| text-overflow |
| clip | ellipsis |
| clip |
| block containers |
| no |
| N/A |
| as specified keyword |
| per grammar |
| discrete |
This property specifies rendering when inline content overflows its end 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, or writing-mode appropriate ellipsis character, or three dots "..." if the ellipsis character is unavailable.The term "character" is used in this property definition for better readability and means "grapheme cluster" [UAX29] for implementation purposes.
For the ellipsis value implementations must hide characters and atomic inline-level elements at the end edge of the line as necessary to fit the ellipsis, and place the ellipsis immediately adjacent to the end edge of the remaining inline content. The first character or atomic inline-level element on a line must be clipped rather than ellipsed.
Sample CSS:
div { font-family: monospace; white-space: pre; overflow: hidden; width: 9ch; text-overflow: ellipsis; }Sample HTML fragments, renderings, and your browser:
| <div>שלום 123456</div> |
123456 ם…
| |
| <div dir=rtl>שלום 123456</div> |
…456 שלום
|
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:
| <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. | |
| <div style="text-overflow:ellipsis; overflow:hidden"> CSS IS AWESOME, YES </div> | Third, a similar box with an ellipsis representing the clipped text. | |
| <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. |
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.
This section applies to elements with text-overflow other than text-overflow: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.
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:
While the content is being scrolled, implementations may adjust their rendering of ellipses (e.g. align to the box edge rather than line edge).
| cursor |
| [<cursor-image>,]* <cursor-predefined> |
| auto |
| all elements |
| yes |
| N/A |
| as specified, except with any relative URLs converted to absolute |
| per grammar |
| discrete |
This property specifies the type of cursor to be displayed for the pointing device when the cursor’s hotspot is within the element’s border edge.
Note: As per CSS Backgrounds 3 § 4.1 Curve Radii: the border-radius properties, the border edge is affected by border-radius.
In the case of overlapping elements, which element determines the type of cursor is based on hit testing: the element determining the cursor is the one that would receive a click initiated from this position.
Note: The specifics of hit testing are out of scope of this specification. Hit testing will hopefully be defined in a future revision of CSS or HTML.
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. User agents may also ignore the cursor property and display a cursor of their choice to indicate various states of the UA’s user interface, such as a busy cursor when the page is not responding, or a text cursor when the user is performing text selection.
Note: [HTML] defines special handling of image maps for the cursor property.
Values have the following meanings:
<cursor-image> The first (optional) component of the cursor property is a list of image-based cursors. 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 of these author-defined cursors, it must use the keyword-based cursor at the end of the list.A <cursor-image> has the following syntax:
<cursor-image> = <url> <number>{2}?The user agent retrieves the cursor from the resource designated by the URL. 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, including SVG, as defined in [SVG11], in secure static mode or secure animated mode [SVG2], even if it does not have a natural size.
Note: The CSS Working group initially intended support for all SVG, naturally sized or not. Support for non-naturally sized SVG was downgraded from mandatory to optional due to lack of implementations.
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 natural aspect ratio, if any.
The optional pair of <number> values give the X and Y coordinates of the exact position within the image which is the pointer position (i.e., the hotspot), as offsets from the left/top of the image.
Note: This specification does not define how the coordinate systems of the various types of <image> are established, and defers these definitions to [CSS4-IMAGES].
If the values are omitted, then the natural hotspot defined inside the image resource itself is used. If it has no natural hotspot, the top left corner of the image is used, as if 0 0 were provided.
If the X or Y coordinates of the hotspot (whether specified explicitly or taken from the image) fall outside of the cursor image, they must be clamped (independently) to fit.
<cursor-predefined> The mandatory <cursor-predefined> keyword specifies a predefined cursor to use, or the fallback cursor to be used if <url>s were provided and none of them can be successfully used.See § 6.1.1.1 Predefined Cursors for the full set of <cursor-predefined> keywords and their meanings.
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 ([SVG11], 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 hotspot. 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.
The <cursor-predefined> production encompasses a broad selection of predefined cursors, present on most operating systems. Its syntax is:
<cursor-predefined> = 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-outThe <cursor-predefined> keywords have the following meanings and likely renderings:
general purpose cursors auto The UA determines the cursor to display based on the current context: auto behaves as text over selectable text or editable elements, 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. 6.1.1.2. Cursor of the canvasThe document canvas is the infinite surface over which the document is rendered [CSS2]. 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.
Tests| caret-color |
| auto | <color> |
| auto |
| all elements |
| yes |
| N/A |
| The computed value for auto is auto; the computed value of currentColor is currentColor (See currentcolor); see the color property for other <color> values. |
| per grammar |
| color by computed value |
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.
Note: UAs might have additional things that count as “carets”. For example, some UAs can show a “navigation caret”, which acts similarly to an insertion caret but can be moved around in non-editable text, and is functionally a caret. On the other hand, the cursor image shown when hovering over text when the cursor property is auto, or when hovering over an element where the cursor property is text or vertical-text, though it sometimes resembles a caret, is not a caret (it’s a cursor).
"ime-mode" is a property somewhat implemented in some browsers, that is problematic and officially obsoleted by this specification.
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:
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.
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, working on this specification on behalf of Bloomberg, 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, Chris Rebert, François Remy, Andrey Rybka, Simon Sapin, Alexander Savenkov, Sebastian Schnitzenbaumer, Lea Verou, Etan Wexler, David Woolley, Frank Yan, Boris Zbarsky, and Domel.
This appendix is informative.
The W3C TAG is developing a Self-Review Questionnaire: Security and Privacy for editors of specifications to informatively answer.
Per the Questions to Consider
No.
No.
No.
No.
No.
No.
No.
No.
No.
No.
No.
No differently.
No.
This appendix is informative.
The W3C TAG is developing a Self-Review Questionnaire: Security and Privacy for editors of specifications to informatively answer.
Per the Questions to Consider
Yes to loading, but not to execution. The cursor property accepts <image> values which may include URLs to be loaded. These may be SVG documents which may contain scripts, but this specification requires that scripts must not be run.
Yes. The cursor and caret-color properties enable the page to change the display of the cursor and text insertion caret of the user agent’s native UI. In addition the outline-style property’s auto value (and thus outline shorthand) enable the page to potentially display a native focused element outline presentation around any element.
No.
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=password], input[type=image] { display: inline-block; } input[type=button], input[type=reset], input[type=submit], input[type=checkbox], input[type=radio], input, input[type=text], input[type=password], input[type=image] { 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; resize: both; } input[type=hidden] { /* appearance of the HTML hidden text field in particular */ display: none !important; } input[type=image] { 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 } */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:
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.
TestsTests relating to the content of this specification may be documented in “Tests” blocks like this one. Any such block is non-normative.
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.
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.
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.
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.
| content-box | border-box | content-box | all elements that accept width or height | no | N/A | discrete | per grammar | specified value |
| auto | <color> | auto | all elements | yes | N/A | colorby computed value | per grammar | The computed value for auto is auto; the computed value of currentColor is currentColor (See currentcolor); see the color property for other <color> values. |
| [<cursor-image>,]* <cursor-predefined> | auto | all elements | yes | N/A | discrete | per grammar | as specified, except with any relative URLs converted to absolute |
| [ <'outline-color'> || <'outline-style'> || <'outline-width'> ] | see individual properties | all elements | no | N/A | see individual properties | per grammar | see individual properties |
| <color> | invert | invert | all elements | no | N/A | colorby computed value | per grammar | The computed value for invert is invert; the computed value of currentColor is currentColor (See currentcolor); see the color property for other <color> values. |
| <length> | 0 | all elements | no | N/A | lengthby computed value | per grammar | <length> value in absolute units (px or physical).absolute length |
| auto | <border-style> | none | all elements | no | N/A | discrete | per grammar | as specified |
| <line-width> | medium | all elements | no | N/A | lengthby computed value | per grammar | absolute length, snapped as a border width; 0 if the outline style is none. |
| none | both | horizontal | vertical | none | elements with overflow other than visible,that are scroll containers and optionally replaced elements such as images, videos, and iframes | no | N/A | discrete | per grammar | as specified keyword |
| clip | ellipsis | clip | block containers | no | N/A | discrete | per grammar | as specified keyword |
In all current engines.
In all current engines.
In all current engines.
In all current engines.
In no current engines.
In all current engines.
In all current engines.
In all current engines.
In all current engines.
In all current engines.
In all current engines.
In all current engines.
Support:Android Browser4+Baidu Browser13.52+Blackberry Browser10+Chrome10+Chrome for Android148+Edge12+Firefox29+Firefox for Android150+IE8+IE Mobile10+KaiOS Browser2.5+Opera9.5+Opera MiniAllOpera Mobile10+QQ Browser14.9+Safari5.1+Safari on iOS5.0+Samsung Internet4+UC Browser for Android15.5+
Source: caniuse.com as of 2026-05-17
CanIUseSupport:Android Browser2.1+Baidu Browser13.52+Blackberry Browser7+Chrome4+Chrome for Android148+Edge15+Firefox2+Firefox for Android150+IE (limited)8+IE Mobile (limited)10+KaiOS Browser2.5+Opera11.6+Opera MiniNoneOpera Mobile12+QQ Browser14.9+Safari3.1+Safari on iOS3.2+Samsung Internet4+UC Browser for Android15.5+
Source: caniuse.com as of 2026-05-17
CanIUseSupport:Android Browser148+Baidu Browser13.52+Blackberry BrowserNoneChrome4+Chrome for Android148+Edge79+Firefox5+Firefox for Android150+IENoneIE MobileNoneKaiOS Browser3.0+Opera15+Opera MiniNoneOpera Mobile80+QQ Browser14.9+Safari4+Safari on iOSNoneSamsung Internet5.0+UC Browser for Android15.5+
Source: caniuse.com as of 2026-05-17
CanIUseSupport:Android Browser2.1+Baidu Browser13.52+Blackberry Browser7+Chrome4+Chrome for Android148+Edge12+Firefox7+Firefox for Android150+IE6+IE Mobile10+KaiOS Browser2.5+Opera11+Opera MiniAllOpera Mobile12.1+QQ Browser14.9+Safari3.1+Safari on iOS3.2+Samsung Internet4+UC Browser for Android15.5+
Source: caniuse.com as of 2026-05-17
CanIUseSupport:Android Browser148+Baidu Browser13.52+Blackberry BrowserNoneChrome5+Chrome for Android148+Edge14+Firefox4+Firefox for AndroidNoneIE9+IE MobileNoneKaiOS BrowserNoneOpera15+Opera MiniNoneOpera Mobile80+QQ Browser14.9+Safari5+Safari on iOSNoneSamsung InternetNoneUC Browser for Android15.5+
Source: caniuse.com as of 2026-05-17
CanIUseSupport:Android Browser148+Baidu Browser13.52+Blackberry BrowserNoneChrome68+Chrome for Android148+Edge15+Firefox27+Firefox for AndroidNoneIENoneIE MobileNoneKaiOS BrowserNoneOpera55+Opera MiniNoneOpera Mobile80+QQ Browser14.9+Safari11+Safari on iOSNoneSamsung InternetNoneUC Browser for Android15.5+
Source: caniuse.com as of 2026-05-17
CanIUseSupport:Android Browser148+Baidu Browser13.52+Blackberry BrowserNoneChrome37+Chrome for Android148+Edge12+Firefox24+Firefox for AndroidNoneIENoneIE MobileNoneKaiOS BrowserNoneOpera24+Opera MiniNoneOpera Mobile80+QQ Browser14.9+Safari9+Safari on iOSNoneSamsung InternetNoneUC Browser for Android15.5+
Source: caniuse.com as of 2026-05-17
CanIUseSupport:Android Browser148+Baidu Browser13.52+Blackberry BrowserNoneChrome57+Chrome for Android148+Edge79+Firefox53+Firefox for Android150+IENoneIE MobileNoneKaiOS Browser3.0+Opera44+Opera MiniNoneOpera Mobile80+QQ Browser14.9+Safari11.1+Safari on iOS11.3+Samsung Internet7.2+UC Browser for Android15.5+
Source: caniuse.com as of 2026-05-17