W3C

http://www.w3.org/

Web Apps Working Group
http://www.w3.org/2008/webapps/

Semantic Web
http://www.w3.org/standards/semanticweb/

Web Design
http://www.w3.org/standards/webdesign/

Web Content Accessibility Guidelines (WCAG)
http://www.w3.org/TR/2008/REC-WCAG20-20081211/

HTML and CSS
http://www.w3.org/standards/webdesign/htmlcss

CSS Snapshot (2010)
http://www.w3.org/TR/2011/NOTE-css-2010-20110512/

CSS Specifications
http://www.w3.org/standards/techs/css#w3c_all

-- Box Model (original) http://www.w3.org/TR/2007/WD-css3-box-20070809/

Flexible Box Layout Module http://www.w3.org/TR/2012/CR-css3-flexbox-20120918/ --

Candidate Recommendations (new modules)
http://www.w3.org/standards/techs/css#cr

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CSS Backgrounds Module (borders)
http://www.w3.org/TR/2012/CR-css3-background-20120724/

CSS Compositing and Blending Modes Module
http://www.w3.org/TR/2013/WD-compositing-1-20131010/ (little or no support as of 11/6/2013 - demo site) http://css3clickchart.com/#blending-modes

CSS Filter Effects
http://www.w3.org/TR/2013/WD-filter-effects-20130523/

CSS Fonts Module
http://www.w3.org/TR/2013/CR-css-fonts-3-20131003

CSS Generated Content for Paged Media
http://www.w3.org/TR/2003/WD-css3-content-20030514/

CSS Grid Module
http://www.w3.org/TR/2013/WD-css3-grid-layout-20130910/ (support) http://caniuse.com/css-grid

CSS Masking Module
http://www.w3.org/TR/2013/WD-css-masking-1-20131029/ (support) http://caniuse.com/css-masks

CSS Multi-Column Layout
http://www.w3.org/TR/2011/CR-css3-multicol-20110412/

CSS Regions Module
http://www.w3.org/TR/2013/WD-css3-regions-20130528/

CSS Shapes Module
http://www.w3.org/TR/2013/WD-css-shapes-1-20130620/

CSS Speech Module
http://www.w3.org/TR/2012/CR-css3-speech-20120320/

CSS Text Module
http://www.w3.org/TR/2013/WD-css-text-3-20131010/

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CSS Animations
http://www.w3.org/TR/2013/WD-css3-animations-20130219/

CSS Transitions http://www.w3.org/TR/2013/WD-css3-transitions-20130212/

CSS Transforms http://www.w3.org/TR/2012/WD-css3-transforms-20120911/

CSS Web Animations Module
http://www.w3.org/TR/2013/WD-web-animations-20130625/ (info) http://coding.smashingmagazine.com/2011/05/17/an-introduction-to-css3-keyframe-animations/ http://robertnyman.com/2010/05/06/css3-animations/

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CSS Selectors
http://www.w3.org/TR/2011/REC-css3-selectors-20110929/