A simple plugin that lets you add your custom CSS to style the WordPress Admin. Works with WordPress single install and WordPress multisites.
Version 2.0 is updated wtih an Admin interface and can be found in Appearance > Admin CSS MU
Admin CSS MU uses CSSTidy to clean and optionally minify CSS. CSS is only minified while using it. The editor always shows un-minified CSS for easy editing.
Note: If you want to easily add custom CSS on your Login and Front-end as well (along with WordPress Admin), use my Custom Login Admin Front-end CSS plugin instead.