添加 opacity property, and the hsl() , hsla() , rgba() and rgb() functions to create <color> values. It also defines the currentcolor keyword as a valid color.

transparent color is now a real color (thanks to the support for the alpha channel) and is a now an alias for rgba(0,0,0,0.0) .

It deprecates the system-color keywords that shouldn't be used in a production environment anymore .

Adds the support for the XML Namespaces by defining the notion of CSS qualified name , using the ' | ' syntax and adding the @namespace CSS at-rule.

Adds:

• Substring matching attribute selectors, E[attribute^="value"] , E[attribute$="value"] , E[attribute*="value"] .
• New pseudo-classes: :target , :enabled and :disabled , :checked , :indeterminate , :root , :nth-child and :nth-last-child , :nth-of-type and :nth-last-of-type , :last-child , :first-of-type and :last-of-type , :only-child and :only-of-type , :empty ，和 :not .
• Pseudo-elements are now characterized by two colons rather than one: :after becomes ::after , :before becomes ::before , :first-letter becomes ::first-letter ，和 :first-line becomes ::first-line .
• The new general sibling combinator ( h1~pre ).

Extends the former media type ( print , screen , … ) to a full language allowing queries on the device media capabilities like only screen and (color) .

Media queries are not only used in CSS document but also in some attributes of HTML Elements, like the media 属性在 <link> 元素。

Amends the CSS2.1 Font matching algorithm to be closer to what is really implemented.

Adds:

• Support for downloadable fonts via the CSS @font-face at-rule.
• The control of the contextual inter-glyph spacing via the CSS font-kerning 特性。
• The choice of language-specific glyphs via the CSS font-language-override 特性。
• The choice of glyphs with specific OpenType features via the CSS font-feature-settings 特性。
• The control of the aspect ratio to use when fallback fonts are selected via the CSS font-size-adjust 特性。
• The choice of alternative font faces using the CSS font-stretch , font-variant-alternates , font-variant-caps , font-variant-east-asian , font-variant-ligatures , font-variant-numeric ，和 font-variant-position properties. It also extends the related CSS font-variant shorthand property and introduces the @font-feature-values at-rule.
• The control of the automatic generation of an oblique or bold face when none are found via the CSS font-synthesis 特性。

Adds:

• The ability to tweak the box model using the CSS box-sizing 特性。
  At risk: due to insufficient browser support, standardization of the padding-box value may be postponed to the next iteration of this module.
• Allow the styling of forms according their content using the CSS :indeterminate , :default , :valid , :invalid , :in-range , :out-of-range , :required , :optional , :read-only ，和 :read-write pseudo-classes and the ::value , ::choices , ::repeat-item ，和 ::repeat-index pseudo-elements.
  At risk: due to insufficient browser support, standardization of the pseudo-elements ::value , ::choices , ::repeat-item ，和 ::repeat-index may be postponed to the next iteration of this module .
• Support for icons, defined by the CSS icon property simultaneously with the new icon value of the CSS content 特性。
  At risk: due to insufficient browser support, standardization of the icon property and the icon value may be postponed to CSS4.
• Support for the CSS outline-offset property giving more control on the position of the outline.
• Support for the CSS resize property allowing Web authors to control if and how elements should be resized.
• Support for the CSS text-overflow property defining how text overflows, if needed.
  At risk: due to insufficient browser support, the 2-value syntax of this property as well as the support for <string> values may be postponed to the next iteration of this module.
• The ability to define the hotspot of a cursor as well as the new none , context-menu , cell , vertical-text , alias , copy , no-drop , not-allowed , nesw- resize , nwse- resize , col-resize , row-resize , all-scroll , zoom-in , zoom-out , extending the cursor 特性。
• The ability to specify the sequential navigation order (that is the tabbing order ) using the CSS nav-index , nav-up , nav-right , nav-left , nav-down 特性。
  At risk: due to insufficient browser support, standardization of the navigation properties may be postponed to the next iteration of this module.
• The ability to control the usage of an IME editor, using the CSS ime-mode 特性。
  At risk: due to insufficient browser support, standardization of the ime-mode property may be postponed to the next iteration of this module.

Adds:

• Support, on backgrounds, for any type of <image> , and not only for uri() defined ones.
• Support for multiple background images.
• background-repeat space and round values, and for the 2-value syntax of this CSS property.
• background-attachment local 值。
• The CSS background-origin , background-size ，和 background-clip 特性。
• Support for curved border corners, with the CSS border-radius , border-top-left-radius , border-top-right-radius , border-bottom-left-radius ，和 border-bottom-right-radius 特性。
• Support for the use of an <image> as the border with the CSS border-image , border-image-source , border-image-slice , border-image-width , border-image-outset ，和 border-image-repeat 特性。
• Support for shadows of the element with the CSS box-shadow 特性。

Makes initial and inherit keywords usable on any CSS property.

Formally defines the CSS data types of CSS 2.1, that were implicitely defined by their grammar token and some textual precisions.

Adds:

• Definition for new font-relative length units: rem and ch .
• Definition for viewport-relative length units: vw , vh , vmax ，和 vmin .
• Precision about the real size of the absolute length units, which are not really absolute, but defined in relation with the reference pixel .
• Definition for <angle> , <time> , <frequency> , <resolution> .
• Normative value to the definition of <color> , <image> ，和 <position> .
• Definition for the calc() , attr() ，和 toggle() functional notations.
  At risk: due to insufficient browser support, standardization of the calc() , attr() ，和 toggle() functional notations may be postponed to the next iteration of this module .

Adds:

• initial , unset values for properties.
• The CSS all 特性。
• The scoping mechanism.

Clarifies:

• Interaction of media-dependent @import statements and style sheet loading requirements.

Defines the <image> data type.

Extends the url() syntax to support image slices using media fragments.

Adds:

• dppx unit to the <resolution> data type.
• image() function as a more flexible alternative to url() to define an image from an url.
  At risk: due to insufficient browser support, standardization of the image() function may be postponed to the next iteration of this module.
• 支持 linear-gradient() , repeating-linear-gradient() , radial-gradient() and repeating-radial-gradient() .
• The ability to define how a replaced element should fit in its element, using the CSS object-fit 特性。
  At risk: due to insufficient browser support, standardization of the object-fit and property may be postponed to the next iteration of this module.
• The ability to override the resolution and orientation of an external image using the CSS image-resolution and image-orientation 特性。
  At risk : due to insufficient browser support, standardization of the image-resolution and image-orientation properties may be postponed to the next iteration of this module

Extends:

• the CSS text-decoration property by making it a shorthand for the CSS text-decoration-line , text-decoration-color ，和 text-decoration-style properties. And adds the text-decoration-skip ，和 text-underline-position 特性。

Adds:

• Support for East-Asian-script emphasis marks with the CSS text-emphasis , text-emphasis-style , text-emphasis-color ，和 text-emphasis-position 特性。
• Support for script shadows with the CSS text-shadow 特性。

Clarifies:

• The paint order of the decorations.

At risk: due to insufficient browser support, standardization of the text-decoration-skip , line positioning rules and the ability to place both emphasis marks and ruby above the same base text may be postponed to the next iteration of this module .

Adds:

• Support for defining the behavior of decorations, that is borders and background colors or images, when a box is breaked (at a page, column or line-break) with the CSS box-decoration-break 特性。

Extends:

• the CSS text-transform property with the value full-width .
• the CSS text-align property with the value start , end , start end ，和 match-parent for a better support of documents with multiple directionalities of text.
• the CSS text-align property with a <string> value to align on that character. This is useful to align number on the decimal point.
• the CSS word-spacing and letter-spacing properties with range constraints to control flexibility in justification.

Adds:

• Control on how whitespaces are displayed using the CSS text-space-collapse and tab-size 特性。
• Control on line breaks and word boundaries using the CSS line-break , word-break , hyphens , text-wrap , overflow-wrap ，和 text-align-last 特性。
• Control on how justification is happening, in order to support more type of scripts, using the CSS text-justify 特性。
• Control on edge effect using the CSS text-indent and hanging-punctuation 特性。

Adds:

• the support of bi-dimensional transforms to be applied to any element using the CSS transform and transform-origin properties. The supported transforms are: matrix () , translate() , translateX() , translateY() , scale() , scaleX() , scaleY() , rotate() , skewX() ，和 skewY() .
• the support of tri-dimensional transforms to be applied to any element by adding the CSS transform-style , perspective , perspective-origin ，和 backface-visibility properties and extended the transform property with the following transforms are: matrix 3d() , translate3d() , translateZ() , scale3d() , scaleZ() , rotate3d() , rotateX () , rotateY () , rotateZ() ，和 perspective() .

注意： this specification is a merge of CSS 2D-Transforms, CSS 3D-Transforms and SVG transforms.

Extends:

• the image() functional notation to describe the directionality of the image ( rtl or ltr ), allowing for bidi-sensitive images.
• the image-orientation property by adding the keyword from-image , allowing to follow EXIF data stored into images to be considered.

Adds:

• the image-set() functional notation to allow the definition to equivalent images at different resolution allowing for resolution-negotiated selection of images.
• the element() functional notation allowing the use of part of the page as image.
• the cross-fade() functional notation allowing to refer to intermediate images when transitioning between two images and defines the interpolation between two images.
• the conic-gradient() and repeating-conic-gradient() functional notation describing a new type of gradient.
• the image-rendering property that allow to define how resize of the object should be handled.