HTTP/2 200 date: Thu, 09 Oct 2025 20:14:40 GMT content-type: text/html; charset=utf-8 content-length: 2110 last-modified: Wed, 08 Oct 2025 22:11:47 GMT access-control-allow-origin: * etag: W/"68e6e1a3-217f" expires: Thu, 09 Oct 2025 20:24:40 GMT cache-control: max-age=600 content-encoding: gzip x-proxy-cache: MISS x-github-request-id: A88C:161D92:1D560F1:1DA2E15:68E817AF accept-ranges: bytes age: 0 via: 1.1 varnish x-served-by: cache-sjc1000140-SJC x-cache: MISS x-cache-hits: 0 x-timer: S1760040880.030945,VS0,VE91 vary: Accept-Encoding x-fastly-request-id: bb3fb7ef288660ce0878afc6bd93bc9ed50a0f29 strict-transport-security: max-age=31536000; includeSubDomains; preload expect-ct: enforce, max-age=2592000 alt-svc: h3=":443"; ma=86400

CSS Cascading and Inheritance Level 3 Implementation Report

Last updated 2020-08-25

The following new features were added in Level 3:

Feature	Gecko	Blink	WebKit	EdgeHTML
all shorthand	27+	37+	525+	×
initial keyword	19+	28+	532+	12+
unset keyword	27+	41+	601.5+	13+

Version data sourced from caniuse.com and Wikipedia

The following module integrations were defined in Level 3:

Feature	Gecko	Blink	WebKit	EdgeHTML
Media Queries + @import	○	○	○	○
Animations + Cascade	○	○	×	?
Transitions + Cascade	○	○	○	○

Detailed Testing

Tables below include Gecko, Blink, and WebKit results for Level 3 features.

Test	Interop?	Results	Live
all Shorthand
all does not set direction or unicode-bidi	○	3/3 Pass	Test
all does set display	○	3/3 Pass	Test
all: inherit is overridden by subsequent declarations	○	3/3 Pass	Test
all: initial is overridden by subsequent declarations	○	3/3 Pass	Test
all: unset is overridden by subsequent declarations	○	3/3 Pass	Test
initial Keyword
initial sets inherited and uninherited properties to their initial value	○	3/3 Pass	Test
unset Keyword
unset sets inherited properties to inherit, and uninherited properties to their initial value	○	3/3 Pass	Test
unset sets uninherited properties to their initial value despite UA style sheet declarations to the contrary	○	3/3 Pass	Test
Media Queries + @import Integration
@import rules with simple media queries are supported	○	3/3 Pass	Test
Animations + Cascade Integration
Author non-!important is overridden by animation	○	3/3 Pass	Test
Author !important overrides animation	△	2/3 Pass	Test
!important is invalid in @keyframes	○	3/3 Pass	Test
Transitions + Cascade Integration
Transitions work across importance levels	○	3/3 Pass	Test

Untested

The following test could be written in theory, but would require special configuration of the user agent:

• Transitions work across !important levels of user and user-agent origins.

The following tests could be written in theory, but correct behavior is implied by passing the CSS2 user-stylesheet tests together with the Level 3 tests:

• User and user-agent non-!important are overridden by animations
• User and user-agent !important overrides animations