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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:



In Progress: Restructuring this page for 2021.

To Be Updated

The following sections of this page are out of date as of 2021-04-13 and kept only for historical purposes as part of restructuring this page for 2020.

If you have questions about any specific CSS feature, please click through to its bug/metabug and check its actual status there.



  • CSS Houdini - see inside for Houdini implementation thoughts/plan
  • working towards (longer-term)

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)

Conic Gradients


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

CSS Images 3

SVG properties in CSS

This bit from SVG2:

Motion Path

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.

More specs / features in particular TBD.


  • font inflation removed
  • CSS Transform properties (shorthands)


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


See Also