Explorer Exposed! : These CSS bugs are all found only in Internet Explorer, versions 5 and higher. To see the demos properly, they must be viewed in IE, of course.
CSSdoc : This is a draft to bring automatic documentation to CSS files, like its known for JavaScript and PHP files through JavaDoc/DocTags.
Learn by example: cssreference.io is a free visual guide to CSS. It features the most popular properties, and explains them with illustrated and animated examples.