Closure Stylesheets is an extension to CSS that adds variables, functions, conditionals, and mixins to standard CSS. The tool also supports minification, linting, RTL flipping, and CSS class renaming.
For all the wonderful features it provides, CSS does a surprisingly poor job of the fundamentals of page layout. But options for richer, more dynamic pages are on their way, as Peter Gasston explains
Stylebot is a Google Chrome extension that allows you to quickly create and save persistent custom CSS for sites. Check out the walkthrough or watch it in action.
JsFiddle is a playground for web developers, a tool which may be used in many ways. One can use it as an online editor for snippets build from HTML, CSS and JavaScript. The code can then be shared with others, embedded on a blog, etc. Using this approach, JavaScript developers can very easily isolate bugs. We aim to support all actively developed frameworks - it helps with testing compatibility.
