The new Android version, so far called 'L' and most likely winding up being called Lollipop when it will be released, has a new visual style called Material Design.
For Android this change of visual style means that the code base also needs to service both old API deployments (lower than v20) as well as the new ones (v21 and upwards). In effect this means you have to create res/layout-v21 and res/values-v21 directories to customize the layout and modify the styles for the new API.
In your module's build.gradle you have to change the compileSdkVersion to 'android-L' and the targetSdkVersion to 'L'. If you have any dependencies on support-v4 or appcompat-v7 you need to switch those to v21.+ to pick up future updates, such as a different release candidates up to the released version.