FAB Shadow sample for http://androiduiux.com/2015/07/22/make-the-right-fab/

activity_main.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <!--
        The FAB widget inflates a default style which is available in
        /sdk/extras/android/support/design/res/values. As per Material Design
        guidelines, the FAB elevation is 6dp instead of the preset 8dp value.
        Other default FAB values are correct with respect to the specs.
        Thus to get the correct FAB, we only need to override app:elevation.

        NOTE: it is app:elevation and NOT the API 21+ android:elevation.
        NOTE2 : This FAB is not assigned any icon, just a solid colorAccent FAB
    -->

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        app:elevation="6dp" />

</FrameLayout>

styles.xml

<resources>

    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">

        <item name="colorPrimary">@color/color_primary</item>
        <item name="colorPrimaryDark">@color/color_primary_dark</item>
        <item name="colorAccent">@color/color_accent</item>

        <item name="android:windowBackground">@android:color/white</item>
    </style>

</resources>