Android toolbar / appbar shadow

appbar_shadow.xml

<?xml version="1.0" encoding="utf-8"?>
<View
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="@dimen/appbar_elevation"
    android:background="@drawable/appbar_shadow"/>

dimens.xml

<resources>
    <dimen name="appbar_elevation">4dp</dimen>
</resources>

drawable.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
    <size android:height="@dimen/appbar_elevation" />
    <gradient android:angle="270"
              android:startColor="#88333333"
              android:endColor="@android:color/transparent"/>
</shape>