I am using my own child theme for twentyeleven, and I've made some changes to some plugin's css classes in my child style.css. The problem I'm having is that if I add a new css attribute to a class from the plugin's css, then it will make the change. But, if the attribute is already declared in the plugin's css, it relies on that.
How can I make my child theme's style.css take precedence over the plugin's css files?
Here's an example of what happens from firebug (the first css file is from the plugin, the second is from my child theme):