W3schools
Free html xhtml css javascript jquery xml dom xsl xslt rss ajax asp .net php sql tutorials, references, examples for web building.
http://www.w3schools.com/css/css_quiz.asp
Dbaron
Dbaron
http://dbaron.org/css/test/results
Quirksmode
Quirksmode
http://www.quirksmode.org/css/position.html
Kimblim
A list of css selectors and pseudo selectors - and what browsers support what
http://kimblim.dk/css-tests/selectors
Webstandards
The web standards project is a grassroots coalition fighting for standards which ensure simple, affordable access to web technologies for all.
http://www.webstandards.org/action/acid2
Test suite by w3schools
Free html xhtml css javascript dhtml xml dom xsl xslt rss ajax asp ado php sql tutorials, references, examples for web building.
http://www.w3schools.com/css/css_examples.asp
Brunildo
Brunildo
http://www.brunildo.org/test
W3
W3
http://www.w3.org/Style/CSS/Test
W3c tests
w3c tests
http://www.w3.org/style/css/test/