CSS Lint is an open source CSS code quality tool originally written by Nicholas C. Zakas and Nicole Sullivan. It was released in June 2011 at the Velocity conference.
A lint tool performs static analysis of source code and flags patterns that might be errors or otherwise cause problems for the developer.
CSS Lint points out problems with your CSS code. It does basic syntax checking as well as applying a set of rules to the code that look for problematic patterns or signs of inefficiency. The rules are all pluggable, so you can easily write your own or omit ones you don't want.