CSS

CSS is short for Cascading Style Sheets (CSS), and typically includes the full set of Selectors, CSS properties, values, and @-rules supported by browsers.

CSS is one of several web standards.

For documentation on CSS, how to develop for it, use various properties, see:

• https://developer.mozilla.org/en/CSS

CSS

Priorities

The following CSS specs/proposals are a priority.

In Progress: Updating 2018 completions and reprioritizing for 2019

• List from DevRel kept here: http://mozdevs.github.io/devrel-dashboard/ in CSS and Layout sections

2018 Priorities

These are *in progress* 2018 Priorities for CSS features in Firefox.

• Bugzilla: https://bugzilla.mozilla.org/show_bug.cgi?id=1424418
• Some public input: https://twitter.com/t/status/939273644043366400
• Subsequently discussed by the Platform Layout team at Yallhands in Austin, Texas (further adjustments are likely)

Close to shipping

These features have implementations that are already well in progress and thus it is a priority to finish them and ship.

Grid Level 2

Grid Level 2 AKA subgrid (use-cases, a11y implications)

• CSS Grid level 2 (2018-01-31 Resolved to go FPWD) specifically for subgrid
• doing some exploratory implementing, design may (hopefully likely) change accordingly
• see also for quick use-cases / tutorial:
  • http://fantasai.inkedblade.net/style/discuss/subgrid-markup/
• medium mobile potential impact, different grid layouts for different responsive use-cases

Values and Units 3

CSS Values and Units Module Level 3 (CR) metabug

• [ ] calc() function in particular. metabug
• re-prioritize Values and Units 3 once calc fixes have landed.
• [ ] attr function (at risk) — very useful in combination with CSS Shapes, in the context of a CMS

Media Queries

• Media Queries 4 (note: new features in 4), metabug, specifically:
  • interaction features #1035774 per 2017: supported in Microsoft Edge, Chrome, Safari, Opera, and Android browser
• Media Queries 5, metabug, specifically:
  • prefers-reduced-motion #1365045 per supported in WebKit
• Re-evaluate MQ4/5 prioritization after interaction and prefers-reduced-motion features are implemented.
  • full support of numerical comparators (<, <=, =>, >)
  • expansion of negation syntax (and, or, not)
  • 2017-08-02 CSSWG resolved to take to CR
  • Also prefers-reduced-motion from Level 5 (#1365045)
  • watch for mobile uptake, especially for mobile layout

2018 Medium Priorities

2018 medium priorities are "maybe" items that we're not sure we can get to in 2018, but would really like to (had a lot of interest during yallhands).

Containment

• CSS Containment Module Level 1 (FPWD 2017) 'contain' property, size/layout, style, paint. metabug
  • potential impact for mobile layouts, mobile web apps
  • Chrome shipped in 61

2018 Lower Priorities

Features or areas that are lower priority based on a number of factors.

Actively Implementing

Beyond the above priorities, we should continue to actively implement, fix bugs on the following:

• Stylo (metabug)

Flexbox

Mozilla has a pretty solid complete Flexbox (W3C CR, just waiting on feature-interaction tests to go PR) implementation. We are working on some fixes to make it even better, e.g.

• Metabug for to-be-implemented spec changes

Grid

• CSS Grid (CR) metabug
  • lots of work

3D Transforms

• 3D Transform interop / spec changes, 3D transform bugs

Masking

• CSS Masking (W3C CR), metabug
  • another clip-path ticket — path(): https://bugzilla.mozilla.org/show_bug.cgi?id=1246764

Text Decoration

CSS Text Decoration Module Level 3 (2013 CR) (metabug), e.g.:

• focusing on text-decoration-skip https://bugzilla.mozilla.org/show_bug.cgi?id=812990
• text-emphasis (remaining bugs)
• text-underline-position
• What else left for this module? (JS)
  • See "Depends on" in metabug 1221864 (TÇ)

Writing Modes

CSS Writing Modes Level 3 (2015 CR) (metabug)

• 2017-08-04 CSSWG Resolved to publish an updated CR

Fonts Level 3

Wrap-up the few remaining bugs, or declare that we're done (e.g. font-variant as a descriptor?)

• Fonts 3, metabug

Under the hood and related

• Intersection observer (Intent to ship thread)
• Web Animations API (metabug)

Evaluating

Font Rendering Controls

CSS Font Rendering Controls Module Level 1 (ED)

• focusing on font-display descriptor https://bugzilla.mozilla.org/show_bug.cgi?id=1317445 (implemented behind a flag, other browsers too)

Font Loading

CSS Font Loading Module Level 3 https://developer.mozilla.org/en-US/docs/Web/API/CSS_Font_Loading_API shipped in 41

• CSS Font Loading Improvements, Multiple bugs

Other

• font inflation removed
• CSS Transform properties (shorthands)

Related HTML5

HTML5 layout and presentation related work:

• srcset intrinsic size
• ...

Recent CRs

Cascading and Inheritance

• CSS Cascading and Inheritance Level 3 (CR), metabug
  • New features since CSS2.x
    • scoped styles, animations, and transitions in the cascade.

Upcoming CRs

These CRs are expected in 2017:

For all potential CRs:

• Which browsers have openly announced implementations or intent to implement? (links?)

• Box Alignment (see above)

Text Level 3

• Text (need list of changes since CSS 2.1), metabug

Selectors 4

Selectors 4 (need list of changes since 3), metabug

• No explicit dependency on Stylo, just lower priority
• Selectors4 remaining features
  • CSS ::selection fixes + unprefixing
  • ... remaining new features? (JS)

Shipping Soon

As the above priorities get implemented, moving down here to note we're waiting for them to ship.

Image Values and Replaced Content

[1] (CR)

• image() function
• [ ] xywh fragment syntax

Style sheet APIs for Add-ons

• style sheet APIs in add-ons SDK / loading async APIs (to be handled by stylo)

Device Adaptation

CSS Device Adaptation Module Level 1 (WD)

properties

Please add subpages for each (unprefixed) CSS property in alphabetical order.

• ...
• overflow
• ...
• text-overflow
• ...

in development

CSS properties which have not yet made it to a Candidate Recommendation (or later), or are only implemented in the wild in prefixed form.

new pseudo-classes

• ...
• :autofill
• ...

new properties

• ...
• text-size-adjust (-moz-, -ms-, -webkit-)
• ...

2019 Priorities

Resize Observer

• Resize Observer (bugzilla, intent to implement coming)

Container Queries Prerequisites

• This is a high priority to evaluate how workable it is to polyfill/prototype once we have Resize Observer (see above) implemented and working

There's a lot of anecdotal demand for Container Queries / Element Queries. See replies here:

• https://twitter.com/t/status/939273644043366400
• https://twitter.com/t/status/955560233144905733 (strong interest, 100+ retweets!)

We should at least figure out what features / bug fixes we would need to address to even consider something like Container Queries (which we should also give input on)

• WICG cq-usecases effort (view open issues to help contribute)
• one proposal: https://tomhodgins.github.io/element-queries-spec/element-queries.html

Scroll Snap update

• Scroll Snap (CR), metabug
  • Fix related bugs - update to latest version of the spec
  • Chrome Intent to Ship (2018-05-10)
  • Safari 11 / iOS11+ supports, Safari-only demo
  • likely medium impact on mobile

Scroll Anchoring

• Scroll Anchoring (ED): https://bugzilla.mozilla.org/show_bug.cgi?id=1305957

Sizing

CSS Intrinsic & Extrinsic Sizing Module Level 3 (TR WD) metabug

• intrinsic size keywords: fix #567039 & #1055887, and unprefix (#1322780
  • 'min-content', 'max-content' in particular (needs bugzilla links)
  • re-evaluate priority at this point, e.g. 'fit-content' is lower priority
• medium mobile impact from height related properties

Shadow Parts

CSS Shadow Parts

• need: spec link, bugzilla link(s), browser status(es)

2019 Medium Priorities

These are *in progress* 2019 Priorities for CSS features in Firefox.

• Bugzilla: https://bugzilla.mozilla.org/show_bug.cgi?id=1424418
• Some public input: https://twitter.com/t/status/939273644043366400
• Subsequently discussed by the Layout team at Mozlando2018 (further adjustments are likely)

Filter Effects Level 2

• Filter Effects Module Level 2: backdrop-filter
  • backdrop-filter bug (caniuse: only Safari supports)
  • also on Trello Future Backlog

Inline Layout

• CSS Inline Layout Module Level 3 (TR WD), metabug
  • focusing on CSS Initial-letter related features (initial-letter * metabug)
    • one (implementation design) blocker issue: https://github.com/w3c/csswg-drafts/issues/743

Houdini

• CSS Houdini - see inside for Houdini implementation thoughts/plan
• working towards (longer-term)
  • Properties & Values API
  • prerequisites for Paint API (Worklets, parts of Typed OM)
  • parity with: Chrome 65 supporting CSS Paint API by default
  • re-evaluate priority of rest of Houdini at this point and re-sort accordingly

2019 Lower Priorities

Box Alignment

• CSS Box Alignment (WD), metabug
  • all properties for blocks (e.g. 1105571)
  • and some details for flexbox (see metabug 1105570 Depends on)
  • spec CR depends on resolving open css-align-3 issues
• unlikely mobile impact (mobile layouts more likely to use flexbox with box alignment properties)

text-decoration-skip

• Bugzilla: https://bugzilla.mozilla.org/show_bug.cgi?id=812990
• parity with Chrome

Conic Gradients

CSS Conic Gradients

• need: spec link, bugzilla link(s), browser status(es)

Shipped and evaluate follow up

Variable Fonts

Fonts Level 4 for Variable Fonts support in particular:

• Bugzilla for Variable Fonts: https://bugzilla.mozilla.org/show_bug.cgi?id=1302685
  • unlikely mobile impact, do any mobile platforms ship a variable font at all?
• Fonts 4 (TR FPWD 2017), metabug

Reprioritize Fonts Level 4 accordingly once we have Variable Fonts.

Shapes

• CSS Shapes (TR CR 2014, another CR was expected in 2017) metabug
  • shape-outside
• would make mobile use-cases more compelling and closer to native apps

2019 Needs Reprioritizing

These are all items we made progress in 2018 (in some cases shipping features or large portions there of) and need to re-evaluate what’s left (if anything) for 2019

Multi-column

• CSS Multi-column Layout (TR WD), metabug
  • unprefixing, column-span, a11y bug hack removal, column-break
  • Low to no mobile impact, possible tablet impact

(Jen has a demo of bugs / test page at http://labs.jensimmons.com/examples/multicolumn-3-bug-demo.html)

----

Former 2018 Lower Priorities, need re-evaluation for 2019:

CSS Images 3

• CSS Images Module Level 3, (2012 CR), metabug
• cross-fade() -- particularly relevant when animating between images
• image-orientation:none
  • possible mobile use-case: photos, just taken on device
• image-rendering: pixelated
  • mobile use-case: displaying QR codes
• position syntax in radial-gradient()
• low to medium mobile impact

SVG properties in CSS

This bit from SVG2:

• 1383650: Implement SVG geometry properties in CSS

Motion Path

• Motion Path Module Level 1 (TR WD 2017), meta bug
  • Blink: 2015-06-09 intent ship; Chrome 56+
• unlikely mobile impact, do any mobile sites even try to use this? or is it just cosmetic?

CSS Color Level 4

CSS Color Module Level 4 (ED), metabug

• Color improvements (wide gamut, color correction, note CSS color correction preffed off)
• low mobile impact (variable lighting anyway, users use of filters)

Implement correct color management of CSS colors (which is really earlier levels of CSS color).

Better Print Support

Start looking at what specs and features would significantly improve print support. Much of this is testing and bugfixing edgecases of existing features, some of it may require or benefit from new specs/features.

• CSS Paged Media Module Level 3 (old 2013 WD) metabug

More specs / features in particular TBD.

See Also

• CSS/
• CSS/:autofill
• CSS/Houdini
• CSS/text-overflow
• CSS/text-size-adjust

• CSS3
• HTML5
• DOM
• Standards
• Platform
• MDN: CSS home page
• Mozilla DevRel Dashboard - dynamic overview of [META] and other high level bugs in CSS, DOM, DevTools, MDN, Toolkit, etc.
• CSS Working Group Wiki