res/anim/dim.xml

<alpha xmlns:android="http://schemas.android.com/apk/res/android"
    android:fromAlpha="1.0"
    android:toAlpha="0.2"
    android:duration="@integer/dim_animation_duration"
    android:fillAfter="true"
    android:interpolator="@android:anim/decelerate_interpolator"
    />