An open-source CSS Authoring Framework. Uses SASS (similar to lesscss) so you can write cleaner CSS. Has tons of built-in mixins and a very nice CSS sprite generator
With each new release of Windows Internet Explorer, support for the World Wide Web Consortium (W3C) Cascading Style Sheets (CSS) standard has steadily improved. Internet Explorer 6 was the first fully CSS, Level 1-compliant version of Internet Explorer.