Comparison of layout engines (CSS)

The following tables compare CSS compatibility and support for a number of layout engines. Please see the individual products' articles for further information. This article is not all-inclusive or necessarily up-to-date. Unless otherwise specified in footnotes, comparisons are based on the stable versions without any add-ons, extensions or external programs.

Engine Nomenclature

• Trident is the layout engine used in Internet Explorer for Windows.
  Tasman is used in Internet Explorer for Macintosh.
  Gecko in all Mozilla software.
  WebCore provides the HTML layout engine for Mac OS X.
  KHTML for KDE.
  Presto for Opera.
  iCab is a browser for the Mac.

Meaning of Values

"Yes" indicates that the current version of the browser fully supports this property when valid values are used. "No" indicates that this property is completely ignored. "Partial" indicates that the property is understood, but that not all values are supported. Supported values are implemented correctly. "Buggy" indicates that the property is understood, but that it is not implemented correctly in all cases. "Dangerous" indicates that the property is understood, but that deleterious behaviour results. Version numbers, where known, are provided to indicate when support for this feature was added. If support was added in a publicly available unofficial release (such as an alpha or beta version), a red background is used. Proprietary properties are not included.

General overview

See the article Cascading Style Sheets for more information on the different versions of CSS. This table doesn't reference CSS2.0, as CSS2.1 was intended to replace it by correcting or removing a few errors and features rejected by the CSS community. Most of the removed CSS2 features will be made obsolete by CSS3.

	Trident	Tasman	Gecko	WebCore	KHTML	Presto	iCab
CSS1	6.0	0	1.0	85	Yes	7.0	Yes
CSS2.1	Partial	Partial	Mostly	Mostly	Mostly	9.0	Mostly
CSS3	No	No	Slight	Slight	Slight	Slight	Slight

Grammar and rules

			Trident	Tasman	Gecko	WebCore	KHTML	Presto	iCab
CSS2	important	Weight increasing	7.0	0	1.0	85	Yes	7.0	Yes
	/*Comment*/	Comments	3.0	0	1.0	85	Yes	7.0	Yes
	@import	Import stylesheet	4.0	0	1.0	Yes	Yes	7.0	Yes
	@charset	Character set	5.5	?	1.0	0	No	7.0	Yes
	@media	Media-specific rules	5.5	0.9	1.0	Yes	Yes	7.0	3.0
	@page	For paged media	5.5	No	No	No	No	7.0	No
CSS3	@namespace	Namespace declaration	No	No	1.0	Yes	Yes	8.0	No
	@font-face	Define font	5.5	No	No	No	No	No	No

Trident grammar and rule notes

1. @font-face ? Only supports Embedded OpenType (.eot) font format, does not understand the format() identifier.
2. !important ? !important doesn't override rules defined later in the same declaration block prior to IE7.

Tasman grammar and rule notes

1. @font-face ? Versions 5.16 and 5.17 will download fonts specified but not use them. 5.23 no longer downloads the font.

Presto grammar and rule notes

1. @import ? Whilst Gecko, WebCore and iCab download all media stylesheets immediately, Opera only downloads handheld, print, projection and screen media, as well as speech if "voice" feature is enabled and tv, on tv devices. Text browser emulation mode is only a user stylesheet, so it does not switch to tty media type. This is consistent with older text browsers, which do not respect any CSS.

Selectors

			Trident	Tasman	Gecko	WebCore	KHTML	Presto	iCab
Element selectors
CSS2	*	Universal	7.0	0	1.0	85	Yes	7.0	3.0
	E	Element	4.0	0	1.0	85	Yes	7.0	Yes
	E.class	Class	7.0	Buggy	1.0	85	Yes	7.0	Yes
	E#id	ID	4.0	0	1.0	85	Yes	7.0	Yes
CSS3	E	Namespaced	No	No	1.0	No	Yes	8.0	No
Relationship selectors
CSS2	E F	Descendant	4.0	0	1.0	85	Yes	7.0	Yes
	E > F	Child	7.0	0	1.0	85	Yes	7.0	3.0
	E + F	Direct adjacent	7.0	0	1.0	85	Yes	7.0	3.0
CSS3	E ~ F	Indirect adjacent	7.0	0.9	1.7	412	3.3.2	9.0	3.0
Attribute selectors
CSS2	E[attr]	Has	7.0	0.9	1.0	85	Yes	7.0	3.0
	E[attr="value"]	Equals	7.0	0.9	1.0	Yes	Yes	7.0	3.0
	E[attr~="value"]	Contains (space-separated)	7.0	0.9	1.0	Yes	Yes	7.0	3.0
	E[attr|="value"]	Contains (hyphen-separated)	7.0	0.9	1.0	Yes	Yes	7.0	3.0
CSS3	E[attr^="value"]	Begins with	7.0	No	1.0	Yes	3.4	8.02	3.0
	E[attr$="value"]	Ends with	7.0	No	1.0	Yes	3.4	9.0	3.0
	E[attr*="value"]	Contains substring	7.0	No	1.0	Yes	3.4	9.0	3.0
	E[ns|attr]	Namespaced	No	No	1.0	No	3.4	9.0	No
Pseudo-classes
CSS2	E:link	Unvisited hyperlink	3.0	0	1.0	85	Yes	7.0	Yes
	E:visited	Visited hyperlink	3.0	0	1.0	85	Yes	7.0	Yes
	E:active	Active	Partial	0	1.0	85	Yes	7.0	Yes
	E:hover	Mouseover	7.0	0.9	1.0	419.3	Yes	7.0	3.0
	E:focus	Focused	No	0	1.0	Yes	Yes	7.0	Yes
	E:first-child	First child	7.0	0	1.0	85	Yes	7.0	3.0
	E:lang()	Language	No	0	1.2	522	3.4	7.5	3.0
CSS3	E:root	Root	No	0.1	1.0	85	3.4	9.5	No
	E:first-of-type	First child of type	No	0.9	No	522	3.4	9.5	No
	E:last-child	Last child	No	0.9	1.0	Dangerous	3.4	9.5	No
	E:last-of-type	Last child of type	No	0.9	No	Dangerous	3.4	9.5	No
	E:only-child	Only child	No	0.9	1.8	Dangerous	3.4	9.5	No
	E:only-of-type	Only child of type	No	0.9	No	Dangerous	3.4	9.5	No
	E:nth-child	Nth child	No	0.9	No	No	3.4	9.5	No
	E:nth-last-child	Nth last child	No	0.9	No	No	3.4	9.5	No
	E:nth-of-type	Nth child of type	No	0.9	No	No	3.4	9.5	No
	E:nth-last-of-type	Nth last child of type	No	0.9	No	No	3.4	9.5	No
	E:target	Target	No	0.9	1.3	Partial	3.4	9.5	No
	E:empty	Empty	No	0.9	1.8	412	3.4	9.5	No
	E:not()	Negation	No	0.9	1.0	85	3.4	9.5	No
	E:enabled	Enabled state	No	0.9	1.8	522	3.4	9.0	No
	E:disabled	Disabled state	No	0.9	1.8	522	3.4	9.0	No
	E:checked	Checked state	No	No	1.0	522	3.4	9.0	No
	E:indeterminate	Indeterminate state	No	0.9	No	No	No	No	No
	E:default	Default	No	No	1.9	No	No	9.0	No
	E:valid	Valid	No	No	1.8	No	No	9.0	No
	E:invalid	Invalid	No	No	1.8	No	No	9.0	No
	E:in-range	In range	No	No	1.8	No	No	9.0	No
	E:out-of-range	Out of range	No	No	1.8	No	No	9.0	No
	E:required	Required	No	No	No	No	No	9.0	No
	E:optional	Optional	No	No	No	No	No	9.0	No
	E:read-only	Read-only	No	No	Experimental	No	No	9.0	No
	E:read-write	Read and write	No	No	Experimental	No	No	9.0	No
Pseudo-elements
CSS2	E:first-letter	First letter	5.5	0	1.0	85	Yes	7.0	3.0
	E:first-line	First line	5.5	0	1.0	85	Yes	7.0	3.0
	E:before	Before	No	No	1.0	85	Yes	7.0	3.0
	E:after	After	No	No	1.0	85	Yes	7.0	3.0
CSS3	E::before	Double colon notation	No	No	1.5	85	3.4	7.0	Yes
	E::after	Double colon notation	No	No	1.5	85	3.4	7.0	Yes
	E::first-letter	Double colon notation	No	0.9	1.5	85	3.4	7.0	Yes
	E::first-line	Double colon notation	No	0.9	1.5	85	3.4	7.0	Yes
	E::selection	Selection	No	0.9	Experimental	412	3.4	No	No
	E::value	Double colon notation	No	No	No	No	No	No	No
	E::choices	Double colon notation	No	No	No	No	No	No	No
	E::repeat-item	Double colon notation	No	No	No	No	No	No	No
	E::repeat-index	Double colon notation	No	No	No	No	No	No	No
			Trident	Tasman	Gecko	WebCore	KHTML	Presto	iCab

Trident selector notes

1. :active ? :active is for anchor element only.
2. :hover ? :hover is applied for all elements only in standards-compliant mode, not quirks mode [1]. Prior to 7.0, :hover is for anchor element only.
3. .one.two ? only .two class selector was taken into consideration before 7.0.
4. * ? Prior to 7.0 this was treated as a single or no element.

Tasman selector notes

1. :hover ? For anchor element only prior to 0.9.
2. .one.two ? only .two class selector is taken into consideration.

WebCore selector notes

1. :lang() ? Only detected when explicitly present on element being tested, attribute not inherited.
2. :target ? Style doesn't get applied when navigating using back and forward buttons.
3. :last-child & :last-of-type ? will match all siblings, or all siblings of the same type, respectively.
4. :only-child & :only-of-type ? identical behaviour to :first-child & :first-of-type.
5. ::pseudo-element ? Mistakenly also triggers on ::pseudo-class prior to version 416.0.

Properties

		Trident	Tasman	Gecko	WebCore	KHTML	Presto	iCab
Box model
CSS2	margin	4.0	0	1.0	85	Yes	7.0	3.0
	padding	4.0	0	1.0	85	Yes	7.0	3.0
	width	4.0	0	1.0	85	Yes	7.0	3.0
	height	4.0	0	1.0	85	Yes	7.0	3.0
	float	5.0	0	1.0	85	Yes	7.0	3.0
	clear	5.0	0	1.0	85	Yes	7.0	Yes
	display	Partial	Partial	Partial	85	Yes	7.0	Partial
	min-width	7.0	0.9	1.0	416	Yes	7.0	3.0
	max-width	7.0	0.9	1.0	416