CSS3 is a set of standards for the display of web pages. These specifications are broken down into modules. The modules of CSS3 add new features and extend the capabilities of CSS2 and are backward compatible. Setting the standards for CSS3 is an ongoing process and not all browsers have be designed to recognize all the new features.

All modern browsers will recognize CSS2 properties. On the other hand, CSS3 property recognition depends on the browser, the browser version and which particular property. In addition to this, not all browsers will represent the assigned CSS properties in the identical manner.

The CSS3 modules include:

CSS Backgrounds and Borders Module Level 3

The CSS3 Backgrounds and Borders Module extends the CSS2 features of borders and backgrounds. These features include borders that consist of images, boxes with multiple backgrounds, boxes with rounded corners and boxes with box shadows.

The CSS3 Background and Borders Module covers the following properties:

background border border-image
background-color border-color border-image-slice
background-image border-style border-image-width
background-repeat border-width border-image-outset
background-attachment border-radius border-image-repeat
background-clip box-shadow border-image-source

CSS Cascading and Inheritance Level 3

 The Cascading and Inheritance Level 3 module reviews how to combine and collate styles for assigning values to all properties on all of the elements in the document. With cascading and inheritance, values can be propagated for the parent element and the children elements.

The CSS3 Cascading and Inheritance Level 3 Module covers the following topics:

@import declared values filtering
content-type cascaded values  
shorthand properties specified values  
resetting property values computed values  
value processing used values  
  actual values  

CSS Color Module Level 3

The CSS Color Module Level 3 covers color values and properties for foreground color and group opacity.

The CSS Color Module Level 3 covers the following topics:

standard color names    
numerical color values    
RGB & RGBA    

Generated and Replaced Content Module

Fonts Module Level 3

Grid Template Layout Module

Media Queries

Selectors Level 3