I have:
in a file build.gradle
(dependencies)
dependencies {
compile \'com.android.support:cardview-v7:21.0.+\'
}
This error can occur if you do not have CardView in your gradle dependencies (in Android Studio) for the module containing your style (even though you have the dependency in the module where you use the card view). In that case, simply add
compile 'com.android.support:cardview-v7:22.2.1'
(or another version) to build.gradle
for the module containing themes.xml or styles.xml.
Then, you do not need to set a parent on your style, nor do you need a namespace prefix, but can follow the example in tsik's answer, so all you need is