How can I emulate button elevation (shadow) in Android API lower than 21?
<p>I have this minimal Android Studio project with just a button.
I assign the button a shadow with:</p>

<pre><code>android:elevation="3dp"
android:translationZ="3dp"
android:stateListAnimator="@null"
</code></pre>

<p>and I see the shadow in Android Studio Design tab. But I also get a warning in the xml editor </p>

<blockquote>
  <p><em>Atribute ... is only used in API level 21 and higher (current min is 16)</em></p>
</blockquote>

<p>And indeed, button shadow is displayed only in emulators with <code>API level 21 or higher</code>, and it is shown flat, with no shadow at all in emulators with <code>API level lower than 21</code>.</p>

<p>So the concrete question is, how can I emulate the shadow effect in <code>API's lower than 21</code>.</p>

<p><strong>activity_main.xml</strong></p>

<pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
&lt;ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"&gt;

    &lt;LinearLayout
        android:id="@+id/main_layout"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:weightSum="1"&gt;

        &lt;RelativeLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_margin="20dp"
            android:layout_weight="2.24"&gt;

            &lt;Button
                android:id="@+id/my_button"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_centerHorizontal="true"
                android:layout_marginLeft="20dp"
                android:layout_marginBottom="20dp"
                android:elevation="5dp"
                android:translationZ="5dp"
                android:stateListAnimator="@null"
                android:background="@android:color/holo_green_light"
                android:text="BUTTON"/&gt;

        &lt;/RelativeLayout&gt;
    &lt;/LinearLayout&gt;
&lt;/ScrollView&gt;
</code></pre>

<p><strong>MainActivity.java</strong></p>

<pre><code>public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

}
</code></pre>

<p>Button showing shadow, in <code>API 22</code>:
<a href="https://i.stack.imgur.com/NTUrt.png" rel="noreferrer"><img src="https://i.stack.imgur.com/NTUrt.png" alt="enter image description here"></a></p>

<p>Same button not showing shadow, in <code>API 16</code>:
<a href="https://i.stack.imgur.com/jSKKY.png" rel="noreferrer"><img src="https://i.stack.imgur.com/jSKKY.png" alt="enter image description here"></a></p>