Awesome
csstree-validator
Validate CSS according to W3C specs and browser implementations.
Extension highlights wrong properties and values when enabled. Just install the extension and open your CSS file. Validation will be performing in background.
<img width="754" src="https://cloud.githubusercontent.com/assets/6654581/18791374/21b9acd0-81bb-11e6-85cb-a1e150beb495.png">