java/com/android/incallui/commontheme/res/animator/button_state.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
  <item android:state_pressed="true" android:state_enabled="true">
    <set>
      <objectAnimator android:propertyName="translationZ"
        android:duration="100"
        android:valueTo="4dp"
        android:valueType="floatType"/>
      <objectAnimator android:propertyName="elevation"
        android:duration="0"
        android:valueTo="@dimen/incall_call_button_elevation"
        android:valueType="floatType"/>
    </set>
  </item>
  <!-- base state -->
  <item android:state_enabled="true">
    <set>
      <objectAnimator android:propertyName="translationZ"
        android:duration="100"
        android:valueTo="0"
        android:startDelay="100"
        android:valueType="floatType"/>
      <objectAnimator android:propertyName="elevation"
        android:duration="0"
        android:valueTo="@dimen/incall_call_button_elevation"
        android:valueType="floatType" />
    </set>
  </item>
  ...
</selector>