transparent Actionbar with AppCompat-v7 21
<!-- Application theme. -->
<style name="AppTheme" parent="Theme.AppCompat.Light">
<item name="android:actionBarStyle">@style/MyActionBar</item>
<item name="android:windowActionBarOverlay">true</item>
<!-- removes shadow underneath the actionbar -->
<!-- Android < Lollipop -->
<item name="android:windowContentOverlay">@null</item>
<!-- Android >= Lollipop -->
<item name="android:elevation">0dp</item>
<!-- Support library compatibility -->
<item name="actionBarStyle">@style/MyActionBar</item>
<item name="windowActionBarOverlay">true</item>
<!-- removes shadow underneath the actionbar -->
<!-- Android < Lollipop -->
<item name="windowContentOverlay">@null</item>
<!-- Android >= Lollipop -->
<item name="elevation">0dp</item>
</style>
<!-- ACTION BAR STYLES -->
<style name="MyActionBar" parent="@style/Widget.AppCompat.ActionBar">
<item name="android:background">@android:color/transparent</item>
<!-- Support library compatibility -->
<item name="background">@android:color/transparent</item>
</style>